Control system for internal combustion engine

ABSTRACT

A control system for an internal combustion engine having at least one fuel injection valve for injecting fuel to an intake pipe or a combustion chamber of the engine. Intake gas state parameters indicative of a state of the intake gases supplied to the engine are detected. Demand values of the intake gas state parameters are calculated according to operating condition parameters indicative of an operating condition of the engine. The intake gas state is controlled so that the intake gas state parameters coincide with the demand values. A control value is then calculated according to the operating condition parameters and deviations of the intake gas state parameters from the demand values. Accordingly, an amount of fuel injected by the at least one fuel injection valve is controlled according to the control value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control system for an internalcombustion engine and, particularly, to a control system that accuratelycontrols an air-fuel ratio in a combustion chamber of the internalcombustion engine having an exhaust gas recirculation mechanism.

2. Description of the Related Art

Japanese Patent Laid-open No. H08-61112 discloses a control system for adiesel engine having an exhaust gas recirculation mechanism. Accordingto the disclosed control system, a gas amount Gf supplied to acombustion chamber is calculated using a map which is set according to adepressed amount of an accelerator and an engine rotational speed, andan intake air amount Ga is detected by an intake air amount sensor.Further, the intake air amount Ga is subtracted from the gas amount Gfto calculate a recirculated gas flow rate Ge. An air amount Gae inexhaust gases recirculated through the exhaust gas recirculationmechanism is calculated according to the recirculated gas amount Ge andan oxygen concentration OX in the exhaust gases detected by an oxygenconcentration sensor provided in the exhaust system. An air amount Gcylsupplied to the combustion chamber is calculated as (Ga+Gae), and a fuelinjection amount is calculated according to the air amount Gcyl.

With respect to the internal combustion engine, especially to the dieselengine, an emission amount of NOx or particulate matter (PM) has beenstrictly regulated in recent years. Accordingly, it is extremelydifficult to obtain the required performance using the conventionalcontrol method which supplies an excessive amount of air compared to thefuel supply amount. Therefore, it is necessary to appropriately controlthe intake air amount of the engine and the air-fuel ratio of theair-fuel mixture in the combustion chamber.

In the conventional control system described above, a technique, whereina target value of the intake air amount is set according to an engineoperating condition and the actual intake air amount is controlled basedon the target value, is not implemented. Consequently, according to theconventional control system, in recent years it has been difficult toperform the intake air amount control and the fuel supply control whichsatisfy a strict demand of the engine performance.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide a control system for aninternal combustion engine, which more strictly controls the intake gasstate and the air-fuel ratio of an air-fuel mixture in an internalcombustion engine, wherein good operating performance and exhaustcharacteristics are obtained.

To attain the above-described aspect, the present invention provides acontrol system for an internal combustion engine having fuel injectionmeans for injecting fuel to an intake pipe or a combustion chamber ofthe engine. The control system includes intake gas state parameterdetecting means, demand value calculating means, intake gas statecontrol means, and fuel injection control means. The intake gas stateparameter detecting means detects intake gas state parameters (GA, PI)which are indicative of a state of intake gases supplied to the engine.The demand value calculating means calculates demand values (Giades,Pides) of the intake gas state parameters according to operatingcondition parameters (NE, TRQ) which are indicative of an operatingcondition of the engine. The intake gas state control means controls theintake gas state so that the intake gas state parameters (GA, PI)coincide with the demand values (Giades, Pides). The fuel injectioncontrol means calculates a control value (Mfcmd) according to theoperating condition parameters (NE, TRQ) and deviations (δGa, δPi) ofthe intake gas state parameters from the demand values and controls anamount of fuel injected by the fuel injection means according to thecontrol value (Mfcmd).

With the above-described structural configuration, the intake gas stateparameters indicative of the state of the intake gases supplied to theengine are detected, and the demand values of the intake gas stateparameters are calculated according to the operating conditionparameters indicative of the operating condition of the engine. Further,the intake gas state is controlled so that the intake gas stateparameters coincide with the demand values, and the fuel injectionamount is controlled according to the operating condition parameters andthe deviations of the intake gas state parameters from the demandvalues. Therefore, the desired intake gas state according to the engineoperating condition is realized, and the control of the fuel injectionamount suitable for the intake gas state is performed, wherein goodengine operating performance and exhaust characteristics are obtained.

Preferably, the fuel injection control means controls a fuel injectiontiming (φfcmd) of the fuel injection means according to the operatingcondition parameters (NE, TRQ) and the deviations (δGa, δPi) of theintake gas state parameters from the demand values.

With the above-described structural configuration, the fuel injectiontiming of the fuel injection means is controlled according to theoperating condition parameters and the deviations of the intake gasstate parameters from the demand values. Therefore, fuel injectiontiming control suitable for the intake gas state, realized by the intakegas state control, is performed, wherein good engine operatingperformance and exhaust characteristics are obtained.

Preferably, the fuel injection control means includes basic controlvalue calculating means, change rate parameter calculating means,correction value calculating means, and control value calculating means.The basic value calculating means calculates a basic control value(Mfmap) according to the operating condition parameters (NE, TRQ). Thechange rate parameter calculating means calculates change rateparameters (Dmfga, Dmfpi) indicative of change rates of the basiccontrol value according to the operating condition parameters (NE, TRQ).The correction value calculating means calculates correction values(δGa×Dmfga, δPi×Dmfpi) by multiplying the change rate parameters (Dmfga,Dmfpi) by the deviations (δGa, δPi) of the intake gas state parametersfrom the demand values. The control value calculating means calculatesthe control value (Mfcmd) of the fuel injection amount by correcting thebasic control value with the correction values (δGa×Dmfga, δPi×Dmfpi).The fuel injection control means performs the fuel injection controlaccording to the control value (Mfcmd) calculated by the control valuecalculating means.

With the above-described structural configuration, the basic controlvalue and the change rate parameters indicative of the change rates ofthe basic control value are calculated according to the operatingcondition parameters. Also, the correction values are calculated bymultiplying the change rate parameters by the deviations of the intakegas state parameters from the demand values. The control value of thefuel injection amount is calculated by correcting the basic controlvalue with the correction values, and fuel injection control isperformed according to the calculated control value. Therefore, anappropriate control value corresponding to the deviations is obtainedeven if the intake gas state parameters do not completely coincide withthe demand values and accurate fuel injection control is performed.Further, since the correction values are calculated by multiplying thechange rate parameters by the deviations, the number of set-points inthe map used for calculating the fuel injection amount that is suitablefor the actual intake gas state parameter values is reduced.Accordingly, accurate fuel injection control is realized, suppressingthe memory capacity and the manpower for setting the map.

Preferably, the intake gas state parameters are any two of an intakepressure (PI), an intake oxygen partial pressure (PIO), and an intakeinert gas partial pressure (PII). If the engine has an exhaust gasrecirculation mechanism for recirculating exhaust gases to an intakesystem, the intake state parameters are any two of the intake pressure(PI), an intake fresh air flow rate (GA), and a flow rate (GR) ofrecirculated exhaust gases.

By using the above-listed intake gas state parameters, it is possible tocontrol an amount of masses of oxygen and inert gases (gases other thanoxygen) in the combustion chamber to the desired values, therebyperforming appropriate and accurate fuel injection control.

Preferably, an intake gas temperature (TI) is further included in theintake gas state parameters, wherein the control system further includesintake gas temperature reference value calculating means for calculatinga reference value (Tinorm) of the intake gas temperature. As such, thefuel injection control means performs the fuel injection controlaccording to a deviation (δTi) of a detected intake gas temperature (TI)from the reference value (Tinorm).

With the above-described structural configuration, the intake gas stateparameters further include the intake gas temperature. Therefore, thefuel injection control is performed in view of any influence fromchanges in the intake gas temperature, thereby improving accuracy of thefuel injection control.

Preferably, the control system further includes combustion modedetermining means for determining a combustion mode (Mdcmb) of theengine according to the operating condition parameters, wherein the fuelinjection control means calculates the control value (Mfcmd) using acontrol map set corresponding to the combustion mode.

With the above-described structural configuration, the combustion modeof the engine is determined according to the operating conditionparameter, and a calculation of the control value is performed using thecontrol map which is set corresponding to the determined combustionmode. That is, a plurality of the combustion modes, which are differentin the air-fuel ratio or the fuel injection timing, are selectedaccording to the engine operating condition, and the control mapcorresponding to the selected combustion mode is used. Accordingly, theoptimal control value is obtained corresponding to each combustion mode.

Preferably, when the combustion mode determining means changes thecombustion mode (Mdcmd), the fuel injection control means uses thecontrol map corresponding to the combustion mode before the change if atleast one of the absolute values of the deviations (δGa, δPi) is equalto or greater than a predetermined threshold value (εga2, εga3, εi2,εpi3). Also, the fuel injection control means uses the control mapcorresponding to the changed combustion mode if each of the absolutevalues of the deviations (δGa, δPi) is less than the predeterminedthreshold value (εga2, εga3, εpi2, εpi3).

With the above-described structural configuration, when the combustionmode is changed, the control map corresponding to the combustion modebefore the change is used if at least one of the absolute values of thedeviations of the intake gas state parameters from the demand values isequal to or greater than the predetermined threshold value, and thecontrol map corresponding to the changed combustion mode is used if eachof the absolute values of the deviations of the intake gas stateparameters is less than the predetermined threshold value. In thetransient state immediately after the combustion mode change, thedeviations of the actual intake gas state parameters from the demandvalues are likely to become large. Therefore, the control mapcorresponding to the combustion mode before the change is used until thedeviations become small. Accordingly, fuel injection control isstabilized.

Preferably, the engine has a throttle valve (3) disposed in the intakepipe, an exhaust gas recirculation mechanism (5, 6) for recirculatingexhaust gases to the intake pipe (2), and a turbo charger (8) having acompressor wheel (15) and a turbine wheel (10). The exhaust gasrecirculation mechanism includes an exhaust gas recirculation passage(5) and an exhaust gas recirculation control valve (6) in the exhaustgas recirculation passage. The turbo charger (8) includes movable vanes(12) for changing a flow rate of exhaust gases injected to the turbinewheel (10). The intake gas state control means controls the intake gasstate by changing openings (TH, LACT, VO) of the throttle valve, exhaustgas recirculation control valve, and movable vanes.

Preferably, the intake gas state control means controls the intake gasstate using a model predictive control.

Preferably, a controlled object model used in the model predictivecontrol is defined using, as control inputs, a mass flow rate (Gv) ofgases passing through the movable vanes, a mass flow rate (Gr) of gasespassing through the exhaust gas recirculation control valve, and a massflow rate (Gth) of fresh air passing through the throttle valve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an internal combustion engine and acontrol system therefore according to a first embodiment of the presentinvention;

FIG. 2 is a block diagram showing a configuration of a control modulefor performing intake gas state control and fuel injection control ofthe internal combustion engine;

FIG. 3 is a block diagram showing a configuration of an intake gas stateparameter demand value setting block shown in FIG. 2;

FIG. 4 is a block diagram showing a configuration of an intake gas statecontrol block shown in FIG. 2;

FIG. 5 is a block diagram showing a configuration of a demandrecirculated gas pressure calculation block shown in FIG. 4;

FIG. 6 is a block diagram showing a configuration of a partial pressureestimation block shown in FIG. 4;

FIG. 7 is a graph of the control output and target value used forexplaining an outline of model predictive control;

FIG. 8 is a block diagram showing a configuration of a model predictivecontroller shown in FIG. 4;

FIGS. 9A-9F are time charts used for illustrating an example of thecontrol operation;

FIG. 10 is a block diagram showing a configuration of a fuel injectioncontrol block shown in FIG. 2;

FIG. 11 is a block diagram showing a first command value calculationblock in FIG. 10;

FIG. 12 is a flowchart of a process for performing intake gas statecontrol and fuel injection control;

FIG. 13 is a flowchart of a process for performing intake gas statecontrol and fuel injection control;

FIG. 14 is a flowchart of a first fuel injection command value mapretrieval process executed in the process of FIG. 13;

FIG. 15 is a schematic diagram of an internal combustion engine and acontrol system therefore according to a second embodiment of the presentinvention;

FIG. 16 is a block diagram showing a configuration of a control modulefor performing intake gas state control and fuel injection control of aninternal combustion engine;

FIG. 17 is a block diagram showing a configuration of an intake gasstate parameter demand value setting block shown in FIG. 16;

FIG. 18 is a block diagram showing a configuration of an intake gasstate control block shown in FIG. 16;

FIG. 19 is a block diagram showing a configuration of a fuel injectioncontrol block shown in FIG. 16.

FIG. 20 is a block diagram showing a first command value calculationblock shown in FIG. 19;

FIG. 21 is a flowchart of a process for performing intake gas statecontrol and fuel injection control;

FIG. 22 is a flowchart of a process for performing intake gas statecontrol and fuel injection control; and

FIG. 23 is a flowchart of a first fuel injection command value map of aretrieval process executed in the process of FIG. 22.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the drawings.

First Embodiment

FIG. 1 is a schematic diagram showing a configuration of an internalcombustion engine and a control system therefore according to a firstembodiment of the present invention. The internal combustion engine 1(hereinafter referred to as “engine”) is a diesel engine wherein fuel isinjected directly into the cylinders. Each cylinder is provided with afuel injection valve 9 electrically connected to an electronic controlunit 20 (hereinafter referred to as “ECU”). The ECU 20 controls a valveopening timing and a valve opening period of each fuel injection valve9.

The engine 1 has an intake pipe 2, an exhaust pipe 4, and a turbocharger8. The turbocharger 8 includes a turbine 11 and a compressor 16. Theturbine 11 has a turbine wheel 10 rotatably driven by the kinetic energyof exhaust gases. The compressor 16 has a compressor wheel 15 connectedto a turbine wheel 10 by a shaft 14. The compressor wheel 15 pressurizes(compresses) the intake air of the engine 1.

The turbine 11 has a plurality of movable vanes 12 (only two areillustrated) and an actuator (not shown) for actuating the movable vanes12 to open and close. The plurality of movable vanes 12 are actuated tochange a flow rate of the exhaust gases injected to the turbine wheel10. The turbine 11 is configured so that the flow rate of the exhaustgases injected to the turbine wheel 10 is changed by adjusting anopening of the movable vane 12 (hereinafter referred to as “vaneopening”) VO, to change the rotational speed of the turbine wheel 10.The actuator, which actuates the movable vanes 12, is connected to theECU 20, and the vane opening VO is controlled by the ECU 20.Specifically, the ECU 20 supplies a control signal of a variable dutyratio to the actuator, wherein the control signal controls the vaneopening VO. The configuration of the turbocharger having movable vanesis known and, for example, disclosed in Japanese Patent Laid-open No.H01-208501.

The intake pipe 2 is provided with an intercooler 18 downstream of thecompressor 16, and a throttle valve 3 downstream of the intercooler 18.The throttle valve 3 is configured to be actuated by an actuator 19 toopen and close. The actuator 19 is connected to the ECU 20. The ECU 20performs an opening control of the throttle valve 3 using the actuator19. A throttle valve opening sensor (not shown) for detecting an openingTH of the throttle valve 3 is provided, and the detection signal of thethrottle valve sensor is supplied to the ECU 20.

An exhaust gas recirculation passage 5 for recirculating exhaust gasesto the intake pipe 2 is provided between the exhaust pipe 4 and theintake pipe 2. The exhaust gas recirculation passage 5 is provided withan exhaust gas recirculation control valve 6 (hereinafter referred to as“EGR valve”) that controls the amount of exhaust gases that arerecirculated. The EGR valve 6 is an electromagnetic valve having asolenoid. A valve opening of the EGR valve 6 is controlled by the ECU20. The EGR valve 6 is provided with a lift sensor 7 for detecting avalve opening (a valve lift amount) LACT, and the detection signal issupplied to the ECU 20. The exhaust gas recirculation passage 5 and theEGR valve 6 form an exhaust gas recirculation mechanism.

An intake air flow rate sensor 21, a boost pressure sensor 22, an intakegas temperature sensor 23, and an intake pressure sensor 24 are disposedin the intake pipe 2. The intake air flow rate sensor 21 detects anintake air flow rate GA. The boost pressure sensor 22 detects an intakepressure PB (boost pressure) at a portion of the intake pipe 2downstream of the compressor 16. The intake gas temperature sensor 23detects an intake gas temperature TI. The intake pressure sensor 24detects an intake pressure PI. Further, an exhaust pressure sensor 25 isdisposed in the exhaust pipe 4. The exhaust pressure sensor 25 detectsan exhaust pressure PE at a portion of the exhaust pipe 4 upstream ofthe turbine 11. The sensors 21 to 25 are connected to the ECU 20, andthe detection signals from the sensors 21 to 25 are supplied to the ECU20.

A catalytic converter 31 and a particulate filter 32 are disposed in theexhaust pipe 4 downstream of the turbine 11. The catalytic converter 31accelerates oxidation of hydrocarbon and CO in the exhaust gases. Theparticulate filter 32 traps particulate matter which mainly consists ofsoot.

An accelerator sensor 27, an engine rotational speed sensor 28, and anatmospheric pressure sensor 29 are connected to the ECU 20. Theaccelerator sensor 27 detects an operation amount AP of the accelerator(not shown) of the vehicle driven by the engine 1 (hereinafter referredto as “the accelerator pedal operation amount AP”). The enginerotational speed sensor 28 detects an engine rotational speed NE. Theatmospheric pressure sensor 29 detects an atmospheric pressure PA. Thedetection signals of the sensors 27 to 29 are supplied to the ECU 20.

The ECU 20 includes an input circuit, a central processing unit(hereinafter referred to as “CPU”), a memory circuit, and an outputcircuit. The input circuit performs various functions, including shapingthe waveforms of input signals from the various sensors, correcting thevoltage levels of the input signals to a predetermined level, andconverting analog signal values into digital values. The memory circuitpreliminarily stores various operating programs to be executed by theCPU and stores the results of computations, or the like, by the CPU. Theoutput circuit supplies control signals to the actuator for actuatingthe movable vanes 12 of the turbine 11, the fuel injection valves 9, theEGR valve 6, the actuator 19 for actuating the throttle valve 3, and thelike.

The ECU 20 determines a combustion mode of the engine 1 according to theoperating condition of the engine 1 and calculates a demand fresh airflow rate Giades, a demand intake pressure Pides, and a reference intakegas temperature Tinorm according to the operating condition of theengine 1. The ECU 20 also controls a state of gases (fresh air andrecirculated gases) supplied to the engine 1 (the state of gases ishereinafter referred to as “intake gas state”). Specifically, the ECU 20performs an intake gas state control wherein the vane opening VO, thethrottle valve opening TH, and the lift amount (opening) LACT of the EGRvalve 6 are controlled so that the detected flow rate GA and thedetected intake pressure PI coincide with the demand fresh air flow rateGiades and the demand intake pressure Pides.

Further, the ECU 20 calculates a fuel injection amount command valueMfcmd and a fuel injection timing command value φfcmd for actuating thefuel injection valve 9 according to the engine operating condition anddemand fresh air flow rate Giades, the demand intake pressure Pides, andthe reference intake gas temperature Tinorm to perform a fuel injectioncontrol suitable for the engine operating condition and the intake gasstate.

FIG. 2 is a block diagram showing a configuration of a control modulewhich performs the above-described intake gas state control and fuelinjection control. The function of each block shown in FIG. 2 isactually realized by operation processes executed by the CPU in the ECU20. Maps for calculating various control parameters shown below are setusing a well-known optimizing tool (i.e., computer program) based onpreviously obtained empirical results.

The control module shown in FIG. 2 includes a combustion modedetermination block 41, an intake gas state parameter demand valuesetting block 42, an intake gas state control block 43, and a fuelinjection control block 44. The functions of the functional blocks 41 to43 are described below.

The combustion mode determination block 41 determines a combustion modeof the engine 1 according to the engine rotational speed NE and a demandtorque TRQ. Specifically, the combustion mode determination block 41selects one of a lean combustion mode, a rich combustion mode, and apremix combustion mode, and outputs a combustion mode parameter Mdcmb.In this embodiment, the combustion mode parameter Mdcmb is set to valuesof “1” to “3”, wherein “1” corresponds to the lean combustion mode, “2”corresponds to the rich combustion mode, and “3” corresponds to thepremix combustion mode.

The lean combustion mode is a combustion mode wherein the air-fuel ratioof the air-fuel mixture in the combustion chamber of the engine 1 is setto a value in a lean region with respect to the stoichiometric ratio.The rich combustion mode is a combustion mode wherein the air-fuel ratiois set to a value in the vicinity of the stoichiometric ratio or in arich region with respect to the stoichiometric ratio, and the premixcombustion mode is a combustion mode wherein the air-fuel ratio is setto a value in a range from the stoichiometric ratio to a value of about“20” by increasing the amount of recirculated exhaust gases relative tothe lean combustion mode. In the premix combustion mode, an ignitiondelay time period (i.e., a time period extending from the fuel injectiontiming to the actual ignition timing) becomes longer, and the premixcombustion is performed. The premix combustion mode is selected in thepreviously set premix combustion region, which is an engine operatingregion defined by the engine rotational speed NE and the demand torqueTRQ.

The demand torque TRQ is calculated according to the engine rotationalspeed NE and the accelerator pedal operation amount AP. The demandtorque TRQ is set to increase as the accelerator pedal operation amountAP increases.

The intake gas state parameter demand value setting block 42 sets thedemand fresh air flow rate Giades, the demand intake pressure Pides, andthe reference intake gas temperature Tinorm according to the enginerotational speed NE, the demand torque TRQ, and the combustion modeparameter Mdcmb. Basically, the demand fresh air flow rate Giades andthe demand intake pressure Pides are set to increase as the enginerotational speed NE increases and/or the demand torque TRQ increases.The reference intake gas temperature Tinorm is empirically obtained bydetecting the actual intake gas temperature in the state where thedemand fresh air flow rate Giades and the demand intake pressure Pidesare realized.

The intake gas state control block 43 calculates an opening commandvalue θvcmd (hereinafter referred to as “vane opening command value”) ofthe movable vanes 12, an opening command value θthcmd (hereinafterreferred to as “throttle valve opening command value”) of the throttlevalve 3, and an opening command value θrcmd (hereinafter referred to as“EGR valve opening command value”) of the EGR valve 6 according to thedemand fresh air flow rate Giades, the demand intake pressure Pides, andthe detected parameters of the engine rotational speed NE, the intakeair flow rate GA, the intake pressure PI, the exhaust pressure PE, andthe atmospheric pressure PA. That is, the intake gas state control block43 performs a control wherein the detected intake air flow rate GA andthe detected intake pressure PI converge, respectively, to the demandfresh air flow rate Giades and the demand intake pressure Pides bycontrolling the movable vane opening θvcmd, the throttle valve openingcommand value θthcmd, and the EGR valve opening command value θrcmd.

The fuel injection control block 44 calculates the fuel injection amountcommand value Mfcmd and the fuel injection timing command value φfcmdaccording to the combustion mode parameter Mdcmb, the demand fresh airflow rate Giades, the demand intake pressure Pides, the reference intakegas temperature Tinorm, and the detected parameters of the enginerotational speed NE, the intake air flow rate GA, the intake pressurePI, and the intake gas temperature TI. The fuel injection valve 9 isactuated by the drive signal according to the fuel injection amountcommand value Mfcmd and the fuel injection timing command value φfcmd.

FIG. 3 is a block diagram showing a configuration of the intake gasstate parameter demand value setting block 42. The intake gas stateparameter demand value setting block 42 includes a first demand valuesetting block 101, a second demand value setting block 102, a thirddemand value setting block 103, and switching blocks 104-106. The firstdemand value setting block 101 retrieves a Giades1 map, a Pides1 map,and a Tinorm1 map (none of which are shown) suitable for the leancombustion mode according to the engine rotational speed NE and thedemand torque TRQ to calculate a first demand fresh air flow rateGiades1, a first demand intake pressure Pides1, and a first referenceintake gas temperature Tinorm1. The second demand value setting block102 retrieves a Giades2 map, a Pides2 map, and a Tinorm2 map (none ofwhich are shown) suitable for the rich combustion mode according to theengine rotational speed NE and the demand torque TRQ to calculate asecond demand fresh air flow rate Giades2, a second demand intakepressure Pides2, and a second reference intake gas temperature Tinorm2.The third demand value setting block 103 retrieves a Giades3 map, aPides3 map, and a Tinorm3 map (none of which are shown) suitable for thepremix combustion mode according to the engine rotational speed NE andthe demand torque TRQ to calculate a third demand fresh air flow rateGiades3, a third demand intake pressure Pides3, and a third referenceintake gas temperature Tinorm3.

The switching block 104 selects any one of the first-to-third demandfresh air flow rates Giades1, Giades2, and Giades3 according to thecombustion mode parameter Mdcmb and outputs the selected parameter asthe demand fresh air flow rate Giades. If Mdcmb is equal to “1”, thefirst demand fresh air flow rate Giades1 is selected. If Mdcmb is equalto “2”, the second demand fresh air flow rate Giades2 is selected. IfMdcmb is equal to “3”, the third demand fresh air flow rate Giades3 isselected. Similar switching is also performed in the switching blocks105 and 106. If Mdcmb is equal to “1”, the first demand intake pressurePides1 and the first reference intake gas temperature Tinorm1 areselected. If Mdcmb is equal to “2”, the second demand intake pressurePides2 and the second reference intake gas temperature Tinorm2 areselected. If Mdcmb is equal to “3”, the third demand intake pressurePides3 and the third reference intake gas temperature Tinorm3 areselected.

FIG. 4 is a block diagram showing a configuration of the intake gasstate control block 43. The intake gas state control block 43 includes ademand recirculated gas partial pressure calculation block 51, a targetpower calculation block 53, an actual power estimation block 54, atarget exhaust pressure calculation block 55, a dividing block 52, atarget intake pressure calculation block 56, a multiplying block 57, asubtracting block 58, a partial pressure estimation block 59, a modelpredictive controller 60, a θv conversion block 61, a θth conversionblock 62, and a θr conversion block 63.

The demand recirculated gas partial pressure calculation block 51includes, as shown in FIG. 5, a demand fresh air partial pressurecalculation block 74, a temperature correction block 76, and asubtracting block 77. The demand fresh air partial pressure calculationblock 74 retrieves a Pia map according to the engine rotational speed NEand the demand fresh air flow rate Giades to calculate a demand freshair partial pressure map value Piamapd. A demand fresh air partialpressure is a desired value of the fresh air partial pressure in theintake gases of the engine 1. The Pia map is set according to acondition wherein the intake gas temperature TI is equal to apredetermined temperature TINOR.

A mass Mia of fresh air occupying a volume of one cylinder and a demandfresh air partial pressure map value Piamapd have a relationshipexpressed by equation (1)Piamapd={R×TINOR/(ηv×Vs)}Mia  (1)where “R” is the gas constant, ηv is a volumetric efficiency, and Vs isa volume of the cylinder.

From equation (1), the demand fresh air partial pressure Piadescorresponding to the intake gas temperature TI is given by equation (2).Piades=(TI/TINOR)Piamapd  (2)

The temperature correction block 76 applies the detected intake gastemperature TI to equation (2) to correct the map value Piamapd, therebycalculating the demand fresh air partial pressure Piades. Thesubtracting block 77 subtracts the demand fresh air partial pressurePiades from the demand intake pressure Pides to calculate a demandrecirculated gas partial pressure Pirdes.

Referring again to FIG. 4, the target power calculation block 53retrieves a Wcref map according to the demand intake pressure Pides, thedemand fresh air flow rate Giades, and the atmospheric pressure PA tocalculate a target power Wcref of the compressor 16. The Wcref map isset so that the target power Wcref increases as the demand intakepressure Pides or the demand fresh air flow rate Giades increases, orthe atmospheric pressure PA decreases. The target power Wcref mayalternatively be calculated by equation (3a). The actual powerestimation block 54 applies the detected boost pressure PB and thedetected intake air flow rate GA to equation (3b) to calculate an actualpower estimated value Wcest of the compressor 16

$\begin{matrix}{{Wcref} = {\frac{1}{\eta\;{cmp}}{{Giades} \cdot {cp} \cdot {TA}}\left\{ {\left( \frac{Pides}{PA} \right)^{\frac{{\kappa\; a} - 1}{\kappa\; a}} - 1} \right\}}} & \left( {3a} \right) \\{{Wcest} = {\frac{1}{\eta\;{cmp}}{{GA} \cdot {cp} \cdot {TA}}\left\{ {\left( \frac{PB}{PA} \right)^{\frac{{\kappa\; a} - 1}{\kappa\; a}} - 1} \right\}}} & \left( {3b} \right)\end{matrix}$where ηcmp is an efficiency of the compressor, cp is an isopiesticspecific heat of air, TA is an atmospheric temperature, and κa is aspecific heat ratio of air.

The target exhaust pressure calculation block 55 calculates the targetexhaust pressure Peref so that the actual power estimated value Wcestcoincides with the target power Wcref. Specifically, when the actualpower estimated value Wcest is smaller than the target power Wcref, thetarget exhaust pressure calculation block 55 updates the target exhaustpressure Peref in the increasing direction, and when the actual powerestimated value Wcest is greater than the target power Wcref, the targetexhaust pressure calculation block 55 updates the target exhaustpressure Peref in the decreasing direction.

The target intake pressure calculation block 56 compares the detectedboost pressure PB with the demand intake pressure Pides and selects thelower pressure to calculate the target intake pressure Piref. Thedividing block 52 divides the demand recirculated gas partial pressurePirdes by the demand intake pressure Pides to calculate a demandrecirculated gas ratio RPIR. The multiplying block 57 multiplies thetarget intake pressure Piref and the demand recirculated gas ratio RPIRto calculate a target recirculated gas partial pressure Pirref. Thesubtracting block 58 subtracts the target recirculated gas partialpressure Pirref from the target intake pressure Piref to calculate atarget fresh air partial pressure Piaref.

As shown in FIG. 6, the partial pressure estimation block 59 includes afresh air partial pressure estimation block 81, a temperature correctionblock 83, and a subtracting block 84. The fresh air partial pressureestimation block 81 calculates a fresh air partial pressure estimationmap value Piamap according to the detected engine rotational speed NEand the detected intake air flow rate GA. The fresh air partial pressureestimation map value Piamap is calculated to increase as the intake airflow rate GA increases, or the engine rotational speed NE decreases.Specifically, the fresh air partial pressure estimation map value Piamapis set to be proportional to the intake air flow rate GA and inverselyproportional to the engine rotational speed NE. The temperaturecorrection block 83 corrects the fresh air partial pressure estimationmap value Piamap according to the detected intake gas temperature TI tocalculate an estimated fresh air partial pressure Piaest like thetemperature correction block 76 shown in FIG. 5. The subtracting block84 subtracts the estimated fresh air partial pressure Piaest from thedetected intake pressure PI to calculate an estimated recirculated gaspartial pressure Pirest.

Referring again to FIG. 4, the model predictive controller 60 calculatesa turbine gas flow rate command value Gvcmd, a fresh air flow ratecommand value Gthcmd, and a recirculated gas flow rate command valueGrcmd using the model predictive control so that the detected exhaustpressure PE, the estimated fresh air partial pressure Piaest, and theestimated recirculated gas partial pressure Pirest coincide,respectively, with the target exhaust pressure Peref, the target freshair partial pressure Piaref, and the target recirculated gas partialpressure Pirref. The turbine gas flow rate command value Gvcmd is acommand value of a flow rate of the gases passing through the turbine11. The fresh air flow rate command value Gthcmd is a command value of aflow rate of fresh air passing through the throttle valve 3, and therecirculated gas flow rate command value Grcmd is a command value of aflow rate of recirculated gases passing through the EGR valve 6.

The θv conversion block 61 converts the turbine gas flow rate commandvalue Gvcmd to an opening command value θv of the movable vane 12(hereinafter referred to as “vane opening command value”) according tothe detected exhaust pressure PE and the detected atmospheric pressurePA. Specifically, the θv conversion block 61 performs the conversion asdescribed below.

The relationship of equation (4) is satisfied by modeling the turbine 11as a nozzle.Gvcmd=Atb(θvcmd)×U(PE)×Φ(PA/PE)  (4)

In equation (4), Atb(θvcmd) is an effective opening area of the movablevanes which is a function of the vane opening, U(PE) is an upstreamcondition function calculated by equation (5), and Φ(PA/PE) is afunction of a ratio of the downstream side pressure and the upstreamside pressure of the movable vane 12. In equation (5), ρe is a densityof the exhaust gases passing through the turbine 11, and in equations(6) and (7), κe is a specific heat ratio of the exhaust gases passingthrough the turbine 11. When the velocity of the flowing exhaust gasesis lower than the acoustic velocity, equation (6) is applied. Equation(7) is applied when the velocity of the flowing exhaust gases is equalto or higher than the acoustic velocity.

$\begin{matrix}{{U({PE})} = \sqrt{2{{PE} \cdot \rho}\; e}} & (5) \\\begin{matrix}{\Phi = \sqrt{\frac{\kappa\; e}{{\kappa\; e} - 1}\left\{ {\left( \frac{PA}{PE} \right)^{\frac{2}{\kappa\; e}} - \left( \frac{PA}{PE} \right)^{\frac{{\kappa\; e} + 1}{\kappa\; e}}} \right\}}} & {\left( \frac{PA}{PE} \right) > \left( \frac{2}{{\kappa\; e} + 1} \right)^{\frac{\kappa\; e}{{\kappa\; e} - 1}}} \\{\Phi = {\left( \frac{2}{{\kappa\; e} + 1} \right)^{\frac{\kappa\; e}{{\kappa\; e} - 1}}\sqrt{\frac{\kappa\; e}{{\kappa\; e} + 1}}}} & {\left( \frac{PA}{PE} \right) \leq \left( \frac{2}{{\kappa\; e} + 1} \right)^{\frac{\kappa\; e}{{\kappa\; e} - 1}}}\end{matrix} & \begin{matrix}(6) \\(7)\end{matrix}\end{matrix}$

The effective opening area Atb(θvcmd) is calculated by equation (8)obtained from equation (4), and the vane opening command value θvcmd iscalculated by retrieving a conversion table previously set according tothe effective opening area Atb(θvcmd).Atb(θvcmd)=Gvcmd/{U(PE)×Φ(PA/PE)}  (8)

The θth conversion block 62 and the θr conversion block 63,respectively, calculate an effective opening area Ath(θth) of thethrottle valve 3 and an effective opening area Ar(θr) of the EGR valve 6by equations (9) and (10), and respectively retrieve conversion tablesaccording to the effective opening areas Ath(θth) and Ar(θr) tocalculate the throttle valve opening command value θthcmd and the EGRvalve opening command value θrcmd.Ath(θthcmd)=Gthcmd/{U(PB)×Φ(PI/PB)}  (9)Ar(θrcmd)=Grcmd/{U(PE)×Φ(PI/PE)}  (10)

U(PB) and Φ(PI/PB) in equation (9), and Φ(PI/PE) in equation (10) aregiven by equations (11) to (15)

$\begin{matrix}{{U({PB})} = \sqrt{2{{PB} \cdot \rho}\; a}} & (11) \\\begin{matrix}{\Phi = \sqrt{\frac{\kappa\; a}{{\kappa\; a} - 1}\left\{ {\left( \frac{PI}{PB} \right)^{\frac{2}{\kappa\; a}} - \left( \frac{PI}{PB} \right)^{\frac{{\kappa\; a} + 1}{\kappa\; a}}} \right\}}} & {\left( \frac{PI}{PB} \right) > \left( \frac{2}{{\kappa\; a} + 1} \right)^{\frac{\kappa\; a}{{\kappa\; a} - 1}}} \\{\Phi = {\left( \frac{2}{{\kappa\; a} + 1} \right)^{\frac{\kappa\; a}{{\kappa\; a} - 1}}\sqrt{\frac{\kappa\; a}{{\kappa\; a} + 1}}}} & {\left( \frac{PI}{PB} \right) \leq \left( \frac{2}{{\kappa\; a} + 1} \right)^{\frac{\kappa\; a}{{\kappa\; a} - 1}}}\end{matrix} & \begin{matrix}(12) \\(13)\end{matrix} \\\begin{matrix}{\Phi = \sqrt{\frac{\kappa\; e}{{\kappa\; e} - 1}\left\{ {\left( \frac{PI}{PE} \right)^{\frac{2}{\kappa\; e}} - \left( \frac{PI}{PE} \right)^{\frac{{\kappa\; e} + 1}{\kappa\; e}}} \right\}}} & {\left( \frac{PI}{PE} \right) > \left( \frac{2}{{\kappa\; e} + 1} \right)^{\frac{\kappa\; e}{{\kappa\; e} - 1}}} \\{\Phi = {\left( \frac{2}{{\kappa\; e} + 1} \right)^{\frac{\kappa\; e}{{\kappa\; e} - 1}}\sqrt{\frac{\kappa\; e}{{\kappa\; e} + 1}}}} & {\left( \frac{PI}{PE} \right) \leq \left( \frac{2}{{\kappa\; e} + 1} \right)^{\frac{\kappa\; e}{{\kappa\; e} - 1}}}\end{matrix} & \begin{matrix}(14) \\(15)\end{matrix}\end{matrix}$where ρa in equation (11) is a density of air, and κa in equation (12)and (13) is the specific heat ratio of air.

The opening of the movable vane 12, the opening of the throttle valve 3,and the opening of the EGR valve 6 are controlled based on the vaneopening command value θvcmd, the throttle valve opening command valueθthcmd, and the EGR valve opening command value θrcmd, respectively,output from the θv conversion block 61, the θth conversion block 62, andthe θr conversion block 63.

Next, the model predictive controller 60 will be explained. First, acontrolled object model obtained by modeling the controlled object ofthe controller 60 is explained.

The relationship between a mass M and a pressure P of gases in a chamberof a volume V is expressed by equation (20) using an absolutetemperature T.PV=MRT  (20)

Equation (21) is obtained by differentiating equation (20) with respectto time

$\begin{matrix}{\frac{\mathbb{d}P}{\mathbb{d}t} = {\kappa\; n\frac{RT}{V}\frac{\mathbb{d}M}{\mathbb{d}t}}} & (21)\end{matrix}$where κn is a polytropic index which takes a value greater than “1.0”and equal to or less than the specific heat ratio κ of the gas in thechamber.

The relationship of equation (21) is applied to the fresh air partialpressure Pia in the intake pipe 2 to obtain equation (22).

$\begin{matrix}{{\frac{\mathbb{d}}{\mathbb{d}t}{Pia}} = {{ki}\left( {{G^{\prime}{th}} - {\frac{Pia}{Pi}G^{\prime}z}} \right)}} & (22)\end{matrix}$where G′th is a fresh air flow rate per unit time period passing throughthe throttle valve 3, G′z is an intake gas flow rate per unit timeperiod flowing into the cylinder and Pi is an intake pressure. Further,the constant ki is given by equation (23)

$\begin{matrix}{{ki} = {\kappa\;{ni}\frac{RTi}{Vi}}} & (23)\end{matrix}$where Ti is an intake gas temperature, Vi is a volume of a portiondownstream of the throttle valve 3 in the intake pipe, and κni is apolytropic index.

Since the intake gas flow rate G′z in equation (22) is expressed byequation (24), equation (22) is expressed by equation (25)

$\begin{matrix}{{G^{\prime}z} = {{{{\frac{NE}{2} \cdot {Pcyl}}\frac{Vcyl}{RTcyl}} \cong {\eta\;{v \cdot \frac{NE}{2} \cdot {Pi}}\frac{Vcyl}{RTi}}} = {k_{\eta\; v}^{\prime}{{Pi}\left( {k_{\eta\; v}^{\prime} = {\frac{{NE}\;\eta\; v}{2} \cdot \frac{Vcyl}{RTi}}} \right)}}}} & (24) \\{{\frac{\mathbb{d}}{\mathbb{d}t}{Pia}} = {{{- k_{\eta\; v}^{\prime}}{{ki} \cdot {Pia}}} + {{{ki} \cdot G^{\prime}}{th}}}} & (25)\end{matrix}$where NE is an engine rotational speed, Pcyl is a pressure in thecylinder, Vcyl is a cylinder volume, Tcyl is a temperature in thecylinder, and ηv is a volumetric efficiency.

In equation (25), the coefficient of the fresh air partial pressure Piais dependent on the engine rotational speed NE. Therefore, equation (25)is converted to an equation based on the crank angle α(specifically,“dt/dα=1/NE” is multiplied with both sides of equation (25)) to obtainequation (26). Gth in equation (26) is a flow rate of fresh air passingthrough the throttle valve 3 per unit crank angle period.

Regarding the recirculated gas partial pressure Pir in the intake pipe,equation (27) is similarly obtained. In equation (27), Gr is a flow rateof recirculated gases passing through the EGR valve 6 per unit crankangle period.

$\begin{matrix}{{\frac{\mathbb{d}}{\mathbb{d}\alpha}{Pia}} = {{{- k_{\eta\; v}}{{ki} \cdot {Pia}}} + {{ki} \cdot {{Gth}\left( {k_{\eta\; v} = {\frac{\eta\; v}{2} \cdot \frac{Vcyl}{RTi}}} \right)}}}} & (26) \\{{\frac{\mathbb{d}}{\mathbb{d}\alpha}{Pir}} = {{{- k_{\eta\; v}}{{ki} \cdot {Pir}}} + {{ki} \cdot {Gr}}}} & (27)\end{matrix}$

On the other hand, equation (28) is satisfied with respect to theexhaust gases on the upstream side of the turbine in the exhaust pipe 4

$\begin{matrix}{{{\frac{\mathbb{d}}{\mathbb{d}t}{Pe}} = {{ke}\left( {{G^{\prime}z} - {G^{\prime}r} - {G^{\prime}v}} \right)}}\left( {{ke} = {\kappa\;{ne}\frac{RTe}{Ve}}} \right)} & (28)\end{matrix}$where Pe is an exhaust pressure on the upstream side of the turbine inthe exhaust pipe 4, G′r is a flow rate of recirculated gases per unittime, G′v is a flow rate of exhaust gases passing through the turbine 11per unit time, Te is a temperature of exhaust gases, Ve is a volume of aportion upstream of the turbine in the exhaust pipe, and κne is apolytropic index.

The intake gas flow rate G′z is expressed by equation (29) bytransforming equation (24).G′z=k′ _(ηv) ×Pi=k′ _(ηv)(Pia+Pir)  (29)

The relationship expressed by equation (29) is applied to equation (28)to obtain equation (30), wherein equation (30) is further transformed toan equation based on the crank angle to obtain equation (31).

$\begin{matrix}{{\frac{\mathbb{d}}{\mathbb{d}t}{Pe}} = {{k_{\eta\; v}^{\prime}{{ke}\left( {{Pia} + {Pir}} \right)}} - {{ke}\left( {{G^{\prime}r} + {G^{\prime}v}} \right)}}} & (30) \\{{\frac{\mathbb{d}}{\mathbb{d}\alpha}{Pe}} = {{k_{\eta\; v}{{ke}\left( {{Pia} + {Pir}} \right)}} - {{ke}\left( {{Gr} + {Gv}} \right)}}} & (31)\end{matrix}$

Equation (32) is obtained by combining equations (26), (27), and (31).

$\begin{matrix}{{\frac{\mathbb{d}}{\mathbb{d}\alpha}\left\lbrack \begin{matrix}{Pia} \\{Pir} \\{Pe}\end{matrix} \right\rbrack} = {{{\left\lbrack \begin{matrix}{{- k_{\eta\; v}}{ki}} & 0 & 0 \\0 & {{- k_{\eta\; v}}{ki}} & 0 \\{k_{\eta\; v}{ke}} & {k_{\eta\; v}{ke}} & 0\end{matrix} \right\rbrack\left\lbrack \begin{matrix}{Pia} \\{Pir} \\{Pe}\end{matrix} \right\rbrack} + {{\left\lbrack \begin{matrix}{ki} & 0 & 0 \\0 & {ki} & 0 \\0 & {- {ke}} & {- {ke}}\end{matrix} \right\rbrack\left\lbrack \begin{matrix}u_{th} \\u_{r} \\u_{v}\end{matrix} \right\rbrack}\mspace{20mu}\begin{bmatrix}u_{th} \\u_{r} \\u_{v}\end{bmatrix}}} = \begin{bmatrix}{Gth} & {Gr} & {Gv}\end{bmatrix}^{T}}} & (32)\end{matrix}$

Next, the controlled object model defined by equation (32) is convertedto a controlled object model of a discrete time system using time kobtained by digitizing analog time t with a sampling period h. Thedigitized controlled object model is defined by equation (34). Thecontrol output x(k), the control input u(k), and the model parametermatrix A and B in equation (34) are expressed by equations (35)-(38).x(k+1)=Ax(k)+Bu(k)  (34)

$\begin{matrix}{{x(k)} = \begin{bmatrix}{{Pia}(k)} \\{{Pir}(k)} \\{{Pe}(k)}\end{bmatrix}} & (35) \\{{u(k)} = \begin{bmatrix}{{Gth}(k)} \\{{Gr}(k)} \\{{Gv}(k)}\end{bmatrix}} & (36) \\{A = \begin{bmatrix}{1 - {{hk}_{\eta\; v}{ki}}} & 0 & 0 \\0 & {1 - {{hk}_{\eta\; v}{ki}}} & 0 \\{{hk}_{\eta\; v}{ke}} & {{hk}_{\eta\; v}{ke}} & 1\end{bmatrix}} & (37) \\{B = \begin{bmatrix}{hki} & 0 & 0 \\0 & {hki} & 0 \\0 & {- {hke}} & {- {hke}}\end{bmatrix}} & (38)\end{matrix}$

FIG. 7 is a graph used for explaining an outline of the model predictivecontrol. In FIG. 7, the control wherein control output x(k) is made tocoincide with a target value (target vector) r is shown. The controloperation is performed using the following method.

1) The output x(k) is measured at the present time k, and the referencetrajectory xR (indicated by the broken line), which is graduallyapproaching the target value r, is calculated.

2) The predicted value xP(k+i) of the future output is calculated usingthe predicting equation, and control inputs u(k), u(k+1), . . . ,u(k+Hu−1) are calculated using the optimizing operation algorithm in thecontrol horizon that is a period of Hu steps (Hu=2 in FIG. 7) after thepresent time k so that the predicted value xP approaches the referencetrajectory xR as nearly as possible in the coincidence horizon.

3) The only one control input u(k) of the calculated control inputsu(k), u(k+1), . . . , u(k+Hu−1) is actually input to the controlledobject.

4) The above steps 1) to 3) are repeated at time (k+1) and thereafter.

Next, the details of the model predictive control are described below.For example, the output x(k+2) is given by equation (39) which isobtained by repeatedly using equation (34). In general, the outputx(k+i), which is an output after a discrete time period i has elapsed,is given by equation (40).x(k+2)=A ² x(k)+ABu(k)+Bu(k+1)  (39)x(k+i)=A ^(i) x(k)+A ^(i−1) Bu(k)+ . . . +Bu(k+i−1)  (40)

The predicted value x(k+i) of the control output x is calculated basedon the assumption that the control input u changes in the controlhorizon from time k to time (k+Hu−1) and thereafter takes a constantvalue. The present control input u(k) is determined so that thepredicted value x(k+i) coincides with the target value in thecoincidence horizon, that is, wherein the value of an evaluationfunction V, which indicates a deviation from the target value, becomesminimum.

In order to determine the control input u(k), the following method isemployed. First, equation (40) is transformed to an equation defined byusing a control input change amount Δu(k), and the optimal control inputchange amount Δu(k)opt is calculated. Second, the optimal control inputchange amount Δu(k)opt is accumulated to calculate the control inputu(k).

The relationship between the control input change amount Δu(k) and thecontrol input u(k) is expressed by equation (41).u(k)=Δu(k)+u(k−1)  (41)

Equations (42) and (43) are obtained by transforming equation (40) usingthe relationship of equation (41). Equation (42) is applied in theperiod wherein the discrete time i is “1” to “Hu”, and equation (43) isapplied in the period wherein the discrete time i is “(Hu+1)” to “Hp”.In equations (42) and (43), “I” is a unit matrix. Equation (44) isobtained by combining equations (42) and (43) in order to be expressedin the form of a matrix and vectors.

$\begin{matrix}{{{x\left( {k + i} \right)} = {{A^{i}{x(k)}} + {\left( {A^{i - 1} + \ldots + A + I} \right)B\;\Delta\;{u(k)}} + \ldots + {B\;\Delta\;{u\left( {k + i - 1} \right)}} + {\left( {A^{i - 1} + \ldots + A + I} \right)B\;{u\left( {k - 1} \right)}}}}\mspace{20mu}\left( {i = {\left. 1 \right.\sim{Hu}}} \right)} & (42) \\{{{x\left( {k + i} \right)} = {{A^{i}{x(k)}} + {\left( {A^{i - 1} + \ldots + A + I} \right)B\;\Delta\;{u(k)}} + \ldots + {\left( {A^{i - {Hu}} + \ldots + A + I} \right)B\;\Delta\;{u\left( {k + {Hu} - 1} \right)}} + {\left( {A^{i - 1} + \ldots + A + I} \right){{Bu}\left( {k - 1} \right)}}}}\mspace{20mu}\left( {i = {{Hu} + {\left. 1 \right.\sim{Hp}}}} \right)} & (43) \\{\begin{bmatrix}{x\left( {k + 1} \right)} \\\vdots \\{x\left( {k + {Hu}} \right)} \\{x\left( {k + {Hu} + 1} \right)} \\\vdots \\{x\left( {k + {Hp}} \right)}\end{bmatrix} = {{\begin{bmatrix}A \\\vdots \\A^{Hu} \\A^{{Hu} + 1} \\\vdots \\A^{Hp}\end{bmatrix}{x( k)}} + {\begin{bmatrix}B \\\vdots \\{\sum\limits_{i = 0}^{{Hu} - 1}{A^{i}B}} \\{\sum\limits_{i = 0}^{Hu}{A^{i}B}} \\\vdots \\{\sum\limits_{i = 0}^{{Hp} - 1}{A^{i}B}}\end{bmatrix}{u\left( {k - 1} \right)}} + \mspace{79mu}{\left\lbrack \begin{matrix}B & \ldots & 0 \\{{AB} + B} & \ldots & 0 \\\vdots & ⋰ & \vdots \\{\sum\limits_{i = 0}^{{Hu} - 1}{A^{i}B}} & \ldots & B \\{\sum\limits_{i = 0}^{Hu}{A^{i}B}} & \ldots & {{AB} + B} \\\vdots & \vdots & \vdots \\{\sum\limits_{i = 0}^{{Hp} - 1}{A^{i}B}} & \ldots & {\sum\limits_{i = 0}^{{Hp} - {Hu}}{A^{i}B}}\end{matrix} \right\rbrack\left\lbrack \begin{matrix}{\Delta\;{u(k)}} \\\vdots \\{\Delta\;{u\left( {k + {Hu} - 1} \right)}}\end{matrix} \right\rbrack}}} & (44)\end{matrix}$

Next, if the evaluation function V is defined by equation (45), equation(45) can be written as equation (49) by defining vectors X(k), T(k), andΔU(k) with equations (46)-(48). In equation (45), Q(i) and R(i) areweighting coefficients, and the weighting matrixes Q and R in equation(49) are provided by equations (50) and (51).

$\begin{matrix}{{V(k)} = {{\sum\limits_{i = {Hw}}^{Hp}{{{x\left( {k + i} \right)} - {r\left( {k + i} \right)}}}_{Q{(i)}}^{2}} + {\sum\limits_{i = 0}^{{Hu} - 1}{{\Delta\;{u\left( {k + i} \right)}}}_{R{(i)}}^{2}}}} & (45) \\{{X(k)} = \begin{bmatrix}{x\left( {k + {Hw}} \right)} \\\vdots \\{x\left( {k + {Hp}} \right)}\end{bmatrix}} & (46) \\{{T(k)} = \begin{bmatrix}{r\left( {k + {Hw}} \right)} \\\vdots \\{r\left( {k + {Hp}} \right)}\end{bmatrix}} & (47) \\{{\Delta\;{U(k)}} = \begin{bmatrix}{\Delta\;{u(k)}} \\\vdots \\{\Delta\;{u\left( {k + {Hu} - 1} \right)}}\end{bmatrix}} & (48) \\{{V(k)} = {{{{X(k)} - {T(k)}}}_{Q}^{2} + {{\Delta\;{U(k)}}}_{R}^{2}}} & (49) \\{Q = \begin{bmatrix}{Q({Hw})} & 0 & \ldots & 0 \\0 & {Q\left( {{Hw} + 1} \right)} & \ldots & \vdots \\\vdots & \vdots & ⋰ & \vdots \\0 & 0 & \ldots & {Q({Hp})}\end{bmatrix}} & (50) \\{R = \begin{bmatrix}{R(0)} & 0 & \ldots & 0 \\0 & {R(1)} & \ldots & \vdots \\\vdots & \vdots & ⋰ & \vdots \\0 & 0 & \ldots & {R\left( {{Hu} - 1} \right)}\end{bmatrix}} & (51)\end{matrix}$

Further, if the coefficient matrixes in equation (44) are expressed byψ, Γ, and Θ as equations (52)-(54), the predicted value vector X(k) inthe coincidence horizon ((k+Hw)−(k+Hp)) is expressed by equation (55).

$\begin{matrix}{\Psi = \begin{bmatrix}A^{Hw} \\\vdots \\A^{Hp}\end{bmatrix}} & (52) \\{\Gamma = \begin{bmatrix}{\sum\limits_{i = 0}^{{Hw} - 1}{A^{i}B}} \\\vdots \\{\sum\limits_{i = 0}^{{Hp} - 1}{A^{i}B}}\end{bmatrix}} & (53) \\{\Theta = \begin{bmatrix}{\sum\limits_{i = 0}^{{Hw} - 1}{A^{i}B}} & \ldots & {\sum\limits_{i = 0}^{{Hw} - {Hu}}{A^{i}B}} \\\vdots & ⋰ & \vdots \\{\sum\limits_{i = 0}^{{Hp} - 1}{A^{i}B}} & \ldots & {\sum\limits_{i = 0}^{{Hp} - {Hu}}{A^{i}B}}\end{bmatrix}} & (54)\end{matrix}$X(k)=Ψx(k)+Γu(k−1)+ΘΔu(k)  (55)

If a tracking error ε(k) is defined by equation (56), the evaluationfunction V of equation (49) is transformed to equation (57).ε(k)=T(k)−Ψx(k)−Γu(k−1)  (56)V(k)=∥ΘΔU(k)−ε(k)∥_(Q) ² +∥ΔU(k)∥_(R) ²   (57)

Further, if matrixes SQ and SR, which correspond respectively to squareroots of the weighting matrixes Q and R, are defined by equations (58)and (59), a squared length of the vector expressed by equation (60)corresponds to the evaluation function V.

$\begin{matrix}{{SQ} = \begin{bmatrix}\sqrt{Q({Hw})} & 0 & \ldots & 0 \\0 & \sqrt{Q\left( {{Hw} + 1} \right)} & \cdots & \vdots \\\vdots & \vdots & ⋰ & \vdots \\0 & 0 & \ldots & \sqrt{Q({Hp})}\end{bmatrix}} & (58) \\{{SR} = \begin{bmatrix}\sqrt{R(0)} & 0 & \ldots & 0 \\0 & \sqrt{R(1)} & \cdots & \vdots \\\vdots & \vdots & ⋰ & \vdots \\0 & 0 & \ldots & \sqrt{R\left( {{Hu} - 1} \right)}\end{bmatrix}} & (59) \\\begin{bmatrix}{{SQ}\left\{ {{{\Theta\Delta}\;{U(k)}} - {ɛ(k)}} \right\}} \\{{SR}\;\Delta\;{U(k)}}\end{bmatrix} & (60)\end{matrix}$

Therefore, the optimal control input change amount vector ΔU(k)opt iscalculated as a control input change amount vector ΔU(k) that makes thelength of the vector expressed by equation (60) minimum. Thiscalculation can be performed with the QR algorism (e.g., refer to“Predictive Control with Constraints” by Jan M. Maciejowski, Japaneseversion published on Jan. 20, 2005 by Tokyo Denki University Press(hereinafter referred to as “document 1”).

If using the expression shown in document 1, the optimal control inputchange amount vector Δu(k)opt is expressed by equations (61), (62), and(63). The back slash included in equation (63) indicates the operationfor calculating the least-square solution. In equation (62), I_(m) is aunit matrix having m-rows and m-columns, and 0 _(m) is a matrix havingm-rows and m-columns whose elements are all “0”. The matrix [I_(m) O_(m)O_(m). . . O_(m)] is a matrix for extracting only the vector Δu(k)optthat is actually used in the calculation of the control input u(k) fromthe vector ΔU(k).

$\begin{matrix}{{\Delta\;{u(k)}{opt}} = {{KMPC} \cdot {ɛ(k)}}} & (61) \\{{KMPC} = {\left\lbrack {l_{m}O_{m}O_{m}\mspace{11mu}\ldots\mspace{11mu} O_{m}} \right\rbrack{KFULL}}} & (62) \\{{KFULL} = {\begin{bmatrix}{{SQ}\;\Theta} \\{SR}\end{bmatrix} \smallsetminus \begin{bmatrix}{SQ} \\0\end{bmatrix}}} & (63)\end{matrix}$

FIG. 8 is a block diagram showing a configuration of the modelpredictive controller 60. The model predictive controller 60 includes atarget value vector calculation block 91, a subtracting block 92, anoptimal input change amount calculation block 93, an accumulation block94, a delay block 95, and a free response output calculation block 96.FIG. 8 shows a configuration in which the control input u(k) is input tothe controlled object 100, and the control output x(k) is fed back tothe model predictive controller 60.

In the present embodiment, the parameter Hu, which determines thecontrol horizon, and the parameter Hw, which determines the start timeof the coincidence horizon, are set to “1”. The parameter Hp, whichdetermines the end time of the coincidence horizon, is set to “2”, andeach of the weighting matrixes Q and R is set to a unit matrix whosediagonal elements are all “1” and other elements are all “0” (i.e., noweighting is substantially applied). Therefore, the matrixes SQ and SR,which are necessary to calculate the optimal input change amountΔu(k)opt, are given by equations (65) and (66), and the matrix Θ isgiven by equation (67). The matrixes ψ and Γ, which are necessary tocalculate the tracking error ε(k), and the target value vector T(k) aregiven by equations (68)-(70).

$\begin{matrix}{{SQ} = \begin{bmatrix}1 & 0 & 0 & 0 & 0 & 0 \\0 & 1 & 0 & 0 & 0 & 0 \\0 & 0 & 1 & 0 & 0 & 0 \\0 & 0 & 0 & 1 & 0 & 0 \\0 & 0 & 0 & 0 & 1 & 0 \\0 & 0 & 0 & 0 & 0 & 1\end{bmatrix}} & (65) \\{{SR} = \begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}} & (66) \\{\Theta = \begin{bmatrix}B \\{AB}\end{bmatrix}} & (67) \\{\Psi = \begin{bmatrix}A \\A^{2}\end{bmatrix}} & (68) \\{\Gamma = \begin{bmatrix}B \\{AB}\end{bmatrix}} & (69) \\{{T(k)} = \begin{bmatrix}{r\left( {k + 1} \right)} \\{r\left( {k + 2} \right)}\end{bmatrix}} & (70)\end{matrix}$

The target value vector calculation block 91 of FIG. 8 calculates thetarget value vector T(k) as follows.

1) The present control deviation e(k) is calculated by equation (71). Inequation (71), s(k) is an input to the target value vector calculationblock 91 and given by equation (72) in this embodiment (hereinafterreferred to as “setting value vector”).

$\begin{matrix}{{e(k)} = {{s(k)} - {x(k)}}} & (71) \\{{S(k)} = \begin{bmatrix}{{Piaref}(k)} \\{{Pirref}(k)} \\{{Peref}(k)}\end{bmatrix}} & (72)\end{matrix}$

2) The control deviation e(k+i) after i steps (after discrete timeperiod i has elapsed) is calculated by equation (73).e(k+i)=λ^(i) ×e(k)  (73)

In equation (73), λ is a parameter indicative of a speed at which theoutput x(k+i) approaches the target value r(k+i) (λ is hereinafterreferred to as “convergence speed parameter”). The convergence speedparameter λ is set to a value between “0” and “1”. The convergence speedbecomes higher as the convergence speed parameter λ is set to a smallervalue.

3) The target value r (k+i) indicating the reference trajectory iscalculated by equation (74).r(k+i)=s(k+i)−e(k+i)  (74)

In this embodiment, the future setting value vector s(k+i) is set to beequal to the present setting value vector s(k) (i.e., the setting valuevector s(k) is constant) and the target value vector T(k) is calculatedby equation (75).

$\begin{matrix}{{T(k)} = \begin{bmatrix}{{{Piaref}(k)} - {\lambda\left( {{{Piaref}(k)} - {{Piaest}(k)}} \right)}} \\{{{Pirref}(k)} - {\lambda\left( {{{Pirref}(k)} - {{Pirest}(k)}} \right)}} \\{{{Peref}(k)} - {\lambda\left( {{{Peref}(k)} - {{PE}(k)}} \right)}} \\{{{Piaref}(k)} - {\lambda^{2}\left( {{{Piaref}(k)} - {{Piaest}(k)}} \right)}} \\{{{Pirref}(k)} - {\lambda^{2}\left( {{{Pirref}(k)} - {{Pirest}(k)}} \right)}} \\{{{Peref}(k)} - {\lambda^{2}\left( {{{Peref}(k)} - {{PE}(k)}} \right)}}\end{bmatrix}} & (75)\end{matrix}$

The delay block 95 delays the control input u(k) by one sampling periodto output the control input u(k−1). The free response output calculationblock 96 applies the control output x(k) and the control input u(k−1) toequation (76) to calculate a free response output xF.XF=Ψx(k)+Γu(k−1)  (76)

Equation (76) is obtained by replacing Δu(k) in equation (55) with “0”,and the free response output xF corresponds to a control output obtainedwhen the control input u(k) is constant.

The subtracting block 92 subtracts the free response output xF from thetarget value vector T(k). The optimal input change amount calculationblock 93 calculates the optimal input change amount Δu(k)opt withequation (56). The accumulation block 94 accumulates the optimal inputchange amount Δu(k)opt to calculate the control input u(k). The modelpredictive controller 60 outputs the calculated control inputu(k)=(Gth(k) Gr(k) Gv(k))^(T) as the fresh air flow rate command valueGthcmd(k), the recirculated gas flow rate command value Grcmd(k), andthe turbine gas flow rate command value Gvcmd(k).

FIGS. 9A-9F are time charts used for illustrating an example of thecontrol operation in this embodiment. FIGS. 9A-9C illustrate changes inthe control input u(k), i.e., Gthcmd(k), Grcmd(k), and Gvcmd(k), andFIGS. 9D-9F illustrate changes in the corresponding control output x(k),i.e., Piaest, Pirest, and PE. At time t1, the EGR valve 6 is opened toincrease the recirculated gas partial pressure Pir in the intake pipe.At the same time, the vane opening of the turbine 11 is controlled toslightly change in the closing direction so as to maintain the exhaustpressure at a constant level. At time t2, the vane opening is controlledto change in the closing direction to increase the exhaust pressure PE,and at the same time, the opening of the EGR valve 6 is controlled toslightly change in the closing direction to maintain the recirculatedgas partial pressure Pie at a constant level. At time t3, the throttlevalve 3 is opened to increase the fresh air partial pressure Pia, and atthe same time, the vane opening is controlled to greatly change in theopening direction to maintain the exhaust pressure PE at a constantlevel.

Thus, according to this embodiment, the fresh air partial pressure Piaand the recirculated gas partial pressure Pir in the intake pipe and theexhaust pressure PE, which are the gas parameters relevant to eachother, independently converge to their corresponding target values.Therefore, the gas parameters are appropriately controlled according tothe operating condition of the engine 1, thereby obtaining the maximumperformance of the engine 1.

According to the intake gas state control block 43, the estimated freshair partial pressure Piaest and the estimated recirculated gas partialpressure Pirest, which are estimated values of the intake gas stateparameters, as well as the target value Peref of the exhaust pressureand the target values Piaref and Pirref of the fresh air partialpressure and recirculated gas partial pressure in the intake pipe, areeach calculated. Further, the vane opening of the turbine 11, theopening of the EGR valve 6, and the opening of the throttle valve 3 arecontrolled using the model predictive control so that the detectedexhaust pressure PE, the estimated fresh air partial pressure Piaest,and the estimated recirculated gas partial pressure Pirest,respectively, coincide with the corresponding target values Peref,Piaref, and Pirref. Consequently, the state of the intake gases isoptimally controlled and the optimal state of the exhaust gases ismaintained.

By using the model predictive control, a plurality of outputs of thecontrolled object having a plurality of inputs and outputs, i.e., theexhaust pressure PE, the fresh air partial pressure Pia, and therecirculated gas partial pressure Pir are made to simultaneouslyconverge to the corresponding target values at the same speed.Consequently, the flow rate control of gases (the fresh air and therecirculated exhaust gases) supplied to the engine is performedcompletely and precisely, thereby obtaining maximum engine performance.Further, if the controlled object model is defined by equations, thecontrol system performing the model predictive control is easilyconfigured. Therefore, the control system is easily applied to varioushardware configurations. In other words, the control system has anadvantage of flexibility and greatly reduces the manpower required forsetting the maps essential for the control.

The demand intake pressure Pides, which is a steady state target valuecorresponding to a steady state of the engine 1, is calculated by thedemand intake pressure calculation block 72 according to the enginerotational speed NE and the demand torque TRQ. The target intakepressure Piref is calculated by selecting the smaller one of thedetected boost pressure PB and the demand intake pressure Pides.Further, the target recirculated gas partial pressure Pirref is set toan available value based on the target intake pressure Piref.Accordingly, the target intake pressure Piref and the targetrecirculated gas partial pressure Pirref are prevented from being set toinappropriate values that are impossible to be controlled due to a delayof change in the boost pressure.

Further, the target power Wcref of the compressor wheel 15 is calculatedaccording to the atmospheric pressure PA, the demand intake pressurePides, and the demand fresh air flow rate Giades. The estimated actualpower Wcest of the compressor wheel 15 is calculated according to thedetected boost pressure PB and the detected fresh air flow rate GA. Thetarget exhaust pressure Peref is calculated so that the estimated actualpower Wcest of the compressor wheel 15 coincides with the target powerWcref. Further, the vane opening, the EGR valve opening, and thethrottle valve opening are calculated so that the detected exhaustpressure PE coincides with the calculated target exhaust pressure Peref.In other words, cascade control is performed wherein the master feedbackcontrol is performed in the calculation of the target exhaust pressurePeref and the slave feedback control is performed in the calculation ofthe control amounts of the flow rate control mechanisms (the movablevanes 12 of the turbine, the EGR valve 6, and the throttle valve 3).Therefore, control performance of the boost pressure control, which hasa relatively low or slow response speed, is improved.

The controlled object model is defined using the mass flow rates Gv, Gr,and Gth of the gases passing through the movable vane 12, the EGR valve6, and the throttle valve 3 as control inputs (i.e., equations(34)-(38)). Therefore, the equations defining the controlled objectmodel are simplified to reduce the calculation load on the CPU in theECU 20, compared with the case where the control amounts of the movablevane 12, the EGR valve 6, and the throttle valve 3 are used as thecontrol inputs. Further, when the flow rate characteristic of themovable vane 12, the EGR valve 6, or the throttle valve 3 is changed,only a change in the conversion characteristic for converting the flowrate to the valve opening is necessary, and no change in the controllogic of the controller 60, which performs the model predictive control,is necessary. Further, by adding a local feedback control wherein theopening of the movable vane 12, the opening of the EGR valve 6, and theopening of the throttle valve 3 are controlled in a feedback manner,control performance against disturbance to the vane opening or the valveopening is improved. The resulting improvement in control performance isan effect of the cascade control which becomes more significant when theresponse speed of the actual valve opening to the valve opening commandvalue is sufficiently fast compared with the behavior of intake gasesand exhaust gases that are the controlled object of the controller 60.

FIG. 10 is a block diagram showing a configuration of the fuel injectioncontrol block 44 of FIG. 2. The fuel injection control block 44 includesa deviation calculation block 111, a transient control block 112, afirst command value calculation block 113, a second command valuecalculation block 114, a third command value calculation block 115, andswitching blocks 116 and 117.

The fuel injection control block 44 calculates the fuel injection amountcommand value Mfcmd and the fuel injection timing command value φfcmdaccording to five input parameters (TRQ, NE, GA, PI, TI). If the methodof calculating the above-discussed command values using a 5-dimensionalmap is adopted, the number of combinations of set-points becomesenormous, making it very difficult to perform the method. In thisembodiment, the method of calculating the fuel injection amount commandvalue Mfcmd and the fuel injection timing command value φfcmd to beoptimal for the values of five input parameters (TRQ, NE, GA, PI, TI)using a plurality of 2-dimensional maps, wherein the demand torque TRQand the engine rotational speed NE are used as input parameters, isadopted.

Specifically, the function f(r,s,x,y,z) defined by five input parametersr, s, x, y, and z is approximated by equation (101)

$\begin{matrix}{{{f\left( {r,s,x,y,z} \right)} \cong {f\left( {r,s} \right)}}❘_{({{xsp},{ysp},{zsp}})}{{{+ \left( {x - {xsp}} \right)}\frac{\partial{f\left( {r,s} \right)}}{\partial x}}❘_{({{xsp},{ysp},{zsp}})}{{{+ \mspace{101mu}\left( {y - {ysp}} \right)}\frac{\partial{f\left( {r,s} \right)}}{\partial y}}❘_{({{xsp},{ysp},{zsp}})}{{{+ \left( {z - {zsp}} \right)}\frac{\partial{f\left( {r,s} \right)}}{\partial z}}❘_{({{xsp},{ysp},{zsp}})}}}}} & (101)\end{matrix}$where, f(r,s)|_((xsp,ysp,zsp)) indicates a value of the function f(r, s)when the parameters x, y, and z are respectively equal to set valuesxsp, ysp, and zsp, and a partial differential coefficient value∂f(r,s)/∂x|_((xsp,ysp,zsp)), and the like, are the same.

In this embodiment, the demand torque TRQ and the engine rotationalspeed NE, respectively, correspond to parameters r and s. The intake airflow rate GA, the intake pressure PI, and the intake gas temperature TI,respectively, correspond to parameters x, y, and z. The demand fresh airflow rate Giades, the demand intake pressure Pides, and the referenceintake gas temperature Tinorm, respectively, correspond to set valuesxsp, ysp, and zsp.

Therefore, by setting f(r,s), ∂f(r,s)/∂x, ∂f(r,s)/∂y, and ∂f(r,s)/∂z,respectively, as a basic value (Mf, φf), a flow rate change rateparameter (Dmfga, Dφfga), a pressure change rate parameter (Dmfpi,Dφfpi), and an intake gas temperature change rate parameter (Dmfti,Dφfti) in maps according to the demand torque TRQ and the enginerotational speed NE, the fuel injection amount command value Mfcmd andthe fuel injection timing command value φfcmd can be obtained byretrieving four 2-dimensional maps and performing the calculation inequation (101).

The fuel injection control block 44 calculates the fuel injection amountcommand value Mfcmd and the fuel injection timing command value φfcmdusing the above-described method.

The deviation calculation block 111 calculates a fresh air flow ratedeviation δGa, an intake pressure deviation δPi, and an intake gastemperature deviation δTi using equations (102)-(104). The deviationscorrespond to (x−xsp), (y−ysp), and (z−zsp) in equation (101).δGa=GA−Giades  (102)δPi=PI−Pides  (103)δTi=TI−Tinorm  (104)

The transient control block 112 calculates a modified combustion modeparameter FMdcmb according to the combustion mode parameter Mdcmb, thefresh air flow rate deviation δGa, and the intake pressure deviationδPi. When the operating condition of the engine 1 is in a steady state,the modified combustion mode parameter FMdcmb is equal to the combustionmode parameter Mdcmb. When the combustion mode parameter Mdcmb ischanged (for example, when changed from “1” to “2”), the modifiedcombustion mode parameter FMdcmb is maintained at the preceding value(“1”) if at least one of the fresh air flow rate deviation δGa and theintake pressure deviation δPi is equal to or greater than apredetermined deviation amount. When both of the fresh air flow ratedeviation δGa and the intake pressure deviation δPi become less than thecorresponding predetermined deviation amounts, the modified combustionmode parameter FMdcmb is set to the changed combustion mode parameterMdcmb (“2”).

The first command value calculation block 113 calculates a first fuelinjection amount Mfcmd1 and a first fuel injection timing φfcmd1suitable for the lean combustion mode according to the demand torqueTRQ, the engine rotational speed NE, the fresh air flow rate deviationδGa, the intake pressure deviation δPi, and the intake gas temperaturedeviation δTi. The second command value calculation block 114 calculatesa second fuel injection amount Mfcmd2 and a second fuel injection timingφfcmd2 suitable for the rich combustion mode according to the demandtorque TRQ, the engine rotational speed NE, the fresh air flow ratedeviation δGa, the intake pressure deviation δPi, and the intake gastemperature deviation δTi. The third command value calculation block 115calculates a third fuel injection amount Mfcmd3 and a third fuelinjection timing φfcmd3 suitable for the premix combustion modeaccording to the demand torque TRQ, the engine rotational speed NE, thefresh air flow rate deviation δGa, the intake pressure deviation δPi,and the intake gas temperature deviation δTi.

The switching block 116 selects any one of the first-to-third fuelinjection amounts Mfcmd1, Mfcmd2, and Mfcmd3 according to the modifiedcombustion mode parameter FMdcmb and outputs the selected one of thefuel injection amounts as the fuel injection amount command value Mfcmd.The switching block 117 selects any one of the first-to-third fuelinjection timings φfcmd1, φfcmd2, and φfcmd3 according to the modifiedcombustion mode parameter FMdcmb and outputs the selected one of thefuel injection timings as the fuel injection timing command value φfcmd.That is, the first fuel injection amount Mfcmd1 and the first fuelinjection timing φfcmd1 are selected when the FMdcmb is equal to “1”,the second fuel injection amount Mfcmd2 and the second fuel injectiontiming φfcmd2 are selected when FMdcmb is equal to “2”, and the thirdfuel injection amount Mfcmd3 and the third fuel injection timing φfcmd3are selected when FMdcmb is equal to “3”.

FIG. 11 is a block diagram showing a configuration of the first commandvalue calculation block 113. The first command value calculation block113 includes first and second basic value calculation blocks 121, 141;first and second flow rate change rate parameter calculation blocks 122,142; first and second pressure change rate parameter calculation blocks123, 143; first and second temperature change rate parameter calculationblocks 124, 144; multiplying blocks 125-127 and 145-147; and addingblocks 128-130 and 148-150.

The first basic value calculation block 121 retrieves a Mf1 mapaccording to the demand torque TRQ and the engine rotational speed NE tocalculate a first fuel injection amount basic value Mf1. The first flowrate change rate parameter calculation block 122 retrieves a Dmfga1 mapaccording to the demand torque TRQ and the engine rotational speed NE tocalculate a first flow rate change rate parameter Dmfga1. The firstpressure change rate parameter calculation block 123 retrieves a Dmfpi1map according to the demand torque TRQ and the engine rotational speedNE to calculate a first pressure change rate parameter Dmfpi1. The firsttemperature change rate parameter calculation block 124 retrieves aDmfti1 map according to the demand torque TRQ and the engine rotationalspeed NE to Calculate a first temperature change rate parameter Dmfti1.

On the above-described Mf1 map, Dmfga1 map, Dmfpi1 map, and Dmfti1 map,values suitable for the lean combustion mode are set, and grid pointsdefined by a value of the demand torque TRQ and the engine rotationalspeed NE are set to be the same as the grid points of the map used inthe first demand value setting block 101.

The multiplying block 125 multiplies the first flow rate change rateparameter Dmfga1 by the fresh air flow rate deviation δGa. Themultiplying block 126 multiplies the first pressure change rateparameter Dmfpi1 by the intake pressure deviation δPi. The multiplyingblock 127 multiplies the first temperature change rate parameter Dmfti1by the intake gas temperature deviation δTi. The adding blocks 128 and129 add the outputs of the multiplying blocks 125-127 to calculate afirst fuel injection amount correction value Mfcr1. The adding block 130adds the first fuel injection amount correction value Mfcr1 to the firstfuel injection amount basic value Mf1 to calculate the first fuelinjection amount Mfcmd1.

The second basic value calculation block 141 retrieves a φf1 mapaccording to the demand torque TRQ and the engine rotational speed NE tocalculate a first fuel injection timing basic value φf1. The second flowrate change rate parameter calculation block 142 retrieves a Dφfga1 mapaccording to the demand torque TRQ and the engine rotational speed NE tocalculate a second flow rate change rate parameter Dφfga1. The secondpressure change rate parameter calculation block 143 retrieves a Dφfpi1map according to the demand torque TRQ and the engine rotational speedNE to calculate a second pressure change rate parameter Dφfpi1. Thesecond temperature change rate parameter calculation block 144 retrievesa Dφfti1 map according to the demand torque TRQ and the enginerotational speed NE to calculate a second temperature change rateparameter Dφfti1.

On the above-described φf1 map, Dφfga1 map, Dφfpi1 map, and Dφfti1 map,values suitable for the lean combustion mode are set, and grid pointsdefined by the demand torque TRQ and the engine rotational speed NE areset to be the same as the grid points of the map used in the firstdemand value setting block 101.

The multiplying block 145 multiplies the second flow rate change rateparameter Dφfga1 by the fresh air flow rate deviation δGa. Themultiplying block 146 multiplies the second pressure change rateparameter Dφfpi1 by the intake pressure deviation δPi. The multiplyingblock 147 multiplies the second temperature change rate parameter Dφfti1by the intake gas temperature deviation δTi. The adding blocks 148 and149 add the outputs of the multiplying blocks 145-147 to calculate afirst fuel injection timing correction value φfcr1. The adding block 150adds the first fuel injection timing correction value φfcr1 to the firstfuel injection timing basic value φf1 to calculate the first fuelinjection timing φfcmd1.

Therefore, the calculations of the first fuel injection amount Mfcmd1and the first fuel injection timing φfcmd1 in the first command valuecalculation block 113 are respectively expressed by equations (105) and(106).

$\begin{matrix}\begin{matrix}{{{Mfcmd}\; 1} = {{{Mf}\; 1} + {{Mfcr}\; 1}}} \\{= {{{Mf}\; 1} + {\delta\;{Ga} \times {Dmfga}\; 1} +}} \\{{\delta\;{Pi} \times {Dmfpi}\; 1} + {\delta\;{Ti} \times {Dmfti}\; 1}}\end{matrix} & (105) \\\begin{matrix}{{\phi\;{fcmd}\; 1} = {{\phi\; f\; 1} + {\phi\;{fcr}\; 1}}} \\{= {{\phi\; f\; 1} + {\delta\;{Ga} \times D\;\phi\;{fga}\; 1} +}} \\{{\delta\;{Pi} \times D\;\phi\;{fpi}\; 1} + {\delta\;{Ti} \times D\;\phi\;{fti}\; 1}}\end{matrix} & (106)\end{matrix}$

The second command value calculation block 114 and the third commandvalue calculation block 115 shown in FIG. 10 are configured similarly asthe first command value calculation block 113. Similarly, the secondfuel injection amount Mfcmd2, the second fuel injection timing φfcmd2,the third fuel injection amount Mfcmd3, and the third fuel injectiontiming φfcmd3 are calculated by equations (107)-(110).

$\begin{matrix}\begin{matrix}{{{Mfcmd}\; 2} = {{{Mf}\; 2} + {{Mfcr}\; 2}}} \\{= {{{Mf}\; 2} + {\delta\;{Ga} \times {Dmfga}\; 2} +}} \\{{\delta\;{Pi} \times {Dmfpi}\; 2} + {\delta\;{Ti} \times {Dmfti}\; 2}}\end{matrix} & (107) \\\begin{matrix}{{\phi\;{fcmd}\; 2} = {{\phi\; f\; 2} + {\phi\;{fcr}\; 2}}} \\{= {{\phi\; f\; 2} + {\delta\;{Ga} \times D\;\phi\;{fga}\; 2} +}} \\{{\delta\;{Pi} \times D\;\phi\;{fpi}\; 2} + {\delta\;{Ti} \times D\;\phi\;{fti}\; 2}}\end{matrix} & (108) \\\begin{matrix}{{{Mfcmd}\; 3} = {{{Mf}\; 3} + {{Mfcr}\; 3}}} \\{= {{{Mf}\; 3} + {\delta\;{Ga} \times {Dmfga}\; 3} +}} \\{{\delta\;{Pi} \times {Dmfpi}\; 3} + {\delta\;{Ti} \times {Dmfti}\; 3}}\end{matrix} & (109) \\\begin{matrix}{{\phi\;{fcmd}\; 3} = {{\phi\; f\; 3} + {\phi\;{fcr}\; 3}}} \\{= {{\phi\; f\; 3} + {\delta\;{Ga} \times D\;\phi\;{fga}\; 3} +}} \\{{\delta\;{Pi} \times D\;\phi\;{fpi}\; 3} + {\delta\;{Ti} \times D\;\phi\;{fti}\; 3}}\end{matrix} & (110)\end{matrix}$

FIGS. 12 and 13 each show a flowchart of a process for executing theabove-described intake gas state control and the fuel injection control.The process is executed at predetermined time intervals (for example, 10milliseconds) by the CPU in the ECU 20.

In step S11, the detected engine rotational speed NE and the demandtorque TRQ are obtained, and the combustion mode parameter Mdcmb isdetermined according to the engine rotational speed NE and the demandtorque TRQ (step S12). If the selected combustion mode is the leancombustion mode, the combustion mode parameter Mdcmb is set to “1”. Ifthe selected combustion mode is the rich combustion mode, the combustionmode parameter Mdcmb is set to “2”. If the selected combustion mode isthe premix combustion mode, the combustion mode parameter Mdcmb is setto “3”.

In step S13, it is determined whether the value of the combustion modeparameter Mcmb is “1”, “2”, or “3”. If the value of the combustion modeparameter Mcmb is “1”, i.e., if the lean combustion mode is selected,the process proceeds to step S14, wherein the Giades1 map, the Pides1map, and the Tinorm1 map are retrieved according to the enginerotational speed NE and the demand torque TRQ to calculate the firstdemand fresh air flow rate Giades1, the first demand intake pressurePides1, and the first reference intake gas temperature Tinorm1. Next,the demand fresh air flow rate Giades, the demand intake pressure Pides,and the reference intake gas temperature Tinorm are set, respectively,to the calculated first demand fresh air flow rate Giades1, the firstdemand intake pressure Pides1, and the first reference intake gastemperature Tinorm1 (step S15).

If the value of the combustion mode parameter Mcmb is “2”, i.e., if therich combustion mode is selected, the process proceeds from step S13 tostep S16, wherein the Giades2 map, the Pides2 map, and the Tinorm2 mapare retrieved according to the engine rotational speed NE and the demandtorque TRQ to calculate the second demand fresh air flow rate Giades2,the second demand intake pressure Pides2, and the second referenceintake gas temperature Tinorm2. Next, the demand fresh air flow rateGiades, the demand intake pressure Pides, and the reference intake gastemperature Tinorm are set, respectively, to the calculated seconddemand fresh air flow rate Giades2, the second demand intake pressurePides2, and the second reference intake gas temperature Tinorm2 (stepS17).

If the value of the combustion mode parameter Mcmb is “3”, i.e., if thepremix combustion mode is selected, the process proceeds from step S13to step S18, wherein the Giades3 map, the Pides3 map, and the Tinorm3map are retrieved according to the engine rotational speed NE and thedemand torque TRQ to calculate the third demand fresh air flow rateGiades3, the third demand intake pressure Pides3, and the thirdreference intake gas temperature Tinorm3. Next, the demand fresh airflow rate Giades, the demand intake pressure Pides, and the referenceintake gas temperature Tinorm are set, respectively, to the calculatedthird demand fresh air flow rate Giades3, the third demand intakepressure Pides3, and the third reference intake gas temperature Tinorm3(step S19).

In step S20, the detected parameters, such as the detected intake airflow rate GA, intake pressure PI, and intake gas temperature TI, areobtained. In step S21, the intake gas state control described above isperformed, and the vane opening command value θvcmd, the throttle valveopening command value θthcmd, and the EGR valve opening command valueθrcmd are calculated.

In step S31 of FIG. 13, the fresh air flow rate deviation δGa, theintake pressure deviation δPi, and the intake gas temperature deviationδTi are calculated. In step S32, like in step S13, it is determinedwhether the value of the combustion mode parameter Mcmb is “1”, “2”, or“3”. If the value of the combustion mode parameter Mcmb is “1”, i.e., ifthe lean combustion mode is selected, the process proceeds to step S33,wherein the modified combustion mode parameter FMdcmb is set to “1”.Thereafter, the process proceeds to step S38.

If the value of the combustion mode parameter Mcmb is “2”, i.e., if therich combustion mode is selected, the process proceeds from step S32 tostep S34, wherein it is determined whether the absolute value of thefresh air flow rate deviation δGa is less than a first predeterminedthreshold value εga2 (for example, 0.05×Giades), and the absolute valueof the intake pressure deviation δPi is less than a second predeterminedthreshold value εpi2 (for example, 0.05×Pides). If the answer to stepS34 is negative (NO), i.e., if |δGa| is greater than or equal to εga2,or |δPi| is greater than or equal to εpi2, the process proceeds to stepS38 without changing the value of the modified combustion mode parameterFMdcmb (holding the preceding value). On the other hand, if the answerto step S34 is affirmative (YES), the modified combustion mode parameterFMdcmb is set to “2” (step S35) and the process proceeds to step S38.

If the value of the combustion mode parameter Mcmb is “3”, i.e., if thepremix combustion mode is selected, the process proceeds from step S32to step S36, wherein it is determined whether the absolute value of thefresh air flow rate deviation δGa is less than a third predeterminedthreshold value εga3 (for example, 0.05×Giades), and the absolute valueof the intake pressure deviation δPi is less than a fourth predeterminedthreshold value εpi3 (for example, 0.05×Pides). If the answer to stepS36 is negative (NO), i.e., if |δGa| is greater than or equal to εga3,or |δPi| is greater than or equal to εpi3, the process proceeds to stepS38 without changing the value of the modified combustion mode parameterFMdcmb (holding the preceding value). On the other hand, if the answerto step S36 is affirmative (YES), the modified combustion mode parameterFMdcmb is set to “3” (step S37) and the process proceeds to step S38.

In step S38, It is determined whether the value of the modifiedcombustion mode parameter FMdcmb is “1”, “2”, or “3”. If the value ofthe modified combustion mode parameter FMdcmb is “1”, a first fuelinjection command value map retrieval process is performed (step S39).If the value of the modified combustion mode parameter FMdcmb is “2”, asecond fuel injection command value map retrieval process is performed(step S40). If the value of the modified combustion mode parameterFMdcmb is “3”, a third fuel injection command value map retrievalprocess is performed (step S41).

FIG. 14 is a flowchart of the retrieval process performed in step S39.

In step S51, the Mf1 map is retrieved according to the engine rotationalspeed NE and the demand torque TRQ to calculate the first fuel injectionamount basic value Mf1. In step S52, a basic fuel injection amount Mfmapis set to the first fuel injection amount basic value Mf1. In step S53,the Dmfga1 map is retrieved according to the engine rotational speed NEand the demand torque TRQ to calculate the first flow rate change rateparameter Dmfga1. In step S54, the flow rate change rate parameter Dmfgais set to the first flow rate change rate parameter Dmfga1.

In step S55, the Dmfpi1 map is retrieved according to the enginerotational speed NE and the demand torque TRQ to calculate the firstpressure change rate parameter Dmfpi1. The pressure change rateparameter Dmfpi is set to the first pressure change rate parameterDmfpi1 in step S56. In step S57, the Dmfti1 map is retrieved accordingto the engine rotational speed NE and the demand torque TRQ to calculatethe first temperature change rate parameter Dmfti1. The temperaturechange rate parameter Dmfti is set to the first temperature change rateparameter Dmfti1 in step S58.

In step S59, the φf1 map is retrieved according to the engine rotationalspeed NE and the demand torque TRQ to calculate the fuel injectiontiming basic value φf1. The basic fuel injection timing φfmap is set tothe fuel injection timing basic value φf1 in step S60. In step S61, theDφfga1 map is retrieved according to the engine rotational speed NE andthe demand torque TRQ to calculate the second flow rate change rateparameter Dφfga1. The flow rate change rate parameter Dφfga is set tothe second flow rate change rate parameter Dφfga1 in step S62.

In step S63, the φfpi1 map is retrieved according to the enginerotational speed NE and the demand torque TRQ to calculate the secondpressure change rate parameter Dφfpi1. The pressure change rateparameter Dφfpi is set to the second pressure change rate parameterDφfpi1 in step S64. In step S65, the Dφfti1 map is retrieved accordingto the engine rotational speed NE and the demand torque TRQ to calculatethe second temperature change rate parameter Dφfti1. The temperaturechange rate parameter Dφfti is set to the second temperature change rateparameter Dφfti1 in step S66.

As described above, the basic fuel injection amount Mfmap, the firstflow rate change rate parameter Dmfga, the first pressure change rateparameter Dmfpi, the first temperature change rate parameter Dmfti, thebasic fuel injection timing φfmap, the second flow rate change rateparameter Dφfga, the second pressure change rate parameter Dφfpi, andthe second temperature change rate parameter Dphifti, all of which aresuitable for the lean combustion mode, are calculated.

Referring back to FIG. 13, the second fuel injection command value mapretrieval process and the third fuel injection command value mapretrieval process of steps S40 and S41 are configured similarly to thefirst fuel injection command value map retrieval process of FIG. 14.That is, in the second fuel injection command value map retrievalprocess, the basic fuel injection amount Mfmap, the first flow ratechange rate parameter Dmfga, the first pressure change rate parameterDmfpi, the first temperature change rate parameter Dmfti, the basic fuelinjection timing φfmap, the second flow rate change rate parameterDφfga, the second pressure change rate parameter Dφfpi, and the secondtemperature change rate parameter Dphifti, all of which are suitable forthe rich combustion mode, are calculated. In the third fuel injectioncommand value map retrieval process, the basic fuel injection amountMfmap, the first flow rate change rate parameter Dmfga, the firstpressure change rate parameter Dmfpi, the first temperature change rateparameter Dmfti, the basic fuel injection timing φfmap, the second flowrate change rate parameter Dφfga, the second pressure change rateparameter Dφfpi, and the second temperature change rate parameter Dφfti,all of which are suitable for the premix combustion mode, arecalculated.

In step S42, the fuel injection amount correction value Mfcr iscalculated by equation (111). In step S43, the fuel injection timingcorrection value φfcr is calculated by equation (112).Mfcr=δGa×Dmfga+δPi×Dmfpi+δTi×Dmfti  (111)φfcr=δGa×Dφfga+δPi×Dφfpi+δTi×Dφfti  (112)

In step S44, the fuel injection amount command value Mfcmd is calculatedby equation (113). In step S45, the fuel injection timing command valueφfcmd is calculated by equation (114).Mfcmd=Mfmap+Mfcr  (113)φfcmd=φfmap+φfcr  (114)

As described above, in this embodiment, the intake air flow rate GA, theintake pressure PI, and the intake gas temperature TI are detected asthe intake gas state parameters indicative of the intake gas state(fresh air and recirculated exhaust gases) of the engine 1, and thedemand values of the intake gas state parameters, i.e., the demand freshair flow rate Giades, the demand intake pressure Pides, and thereference intake gas temperature Tinorm are calculated according to theengine rotational speed NE and the demand torque TRQ which indicate theengine operating condition. The intake gas state is controlled so thatthe intake air flow rate GA and the intake pressure PI coincide,respectively, with the demand fresh air flow rate Giades and the demandintake pressure Pides. Further, the fuel injection amount command valueMfcmd and the fuel injection timing command value φfcmd are calculatedaccording to the engine rotational speed NE, the demand torque TRQ, andthe deviations of the intake air flow rate GA, the intake pressure PI,and the intake gas temperature TI from the corresponding demand values(Giades, Pides) and the reference value (Tinorm), and the fuel injectionvalve 9 is controlled according to the calculated command values.Therefore, the desired intake gas state according to the engineoperating condition is realized, control of the fuel injection amountand the fuel injection timing, which is suitable for the intake gasstate is performed, wherein good engine operating performance andexhaust characteristics are obtained.

Specifically, the basic fuel injection amount Mfmap and the basic fuelinjection timing φfmap are calculated according to the engine rotationalspeed NE and the demand torque TRQ. Further, the first flow rate changerate parameter Dmfga, the first pressure change rate parameter Dmfpi,and the first temperature change rate parameter Dmfti, which indicatethe change rate of the basic fuel injection amount Mfmap, are calculatedaccording to the engine rotational speed NE and the demand torque TRQ.Also, the second flow rate change rate parameter Dφfga, the secondpressure change rate parameter Dφfpi, and the second temperature changerate parameter Dφfti, which indicate the change rate of the basic fuelinjection timing φfmap, are calculated according to the enginerotational speed NE and the demand torque TRQ. Further, the correctionvalues Mfcr and φfcr are calculated by multiplying the fresh air flowrate deviation δGa, the intake pressure deviation δPi, and the intakegas temperature deviation δTi, which indicate the deviations of thedetected intake gas state parameters from the demand values or thereference value, respectively, by the corresponding change rateparameters (Dmfga, Dmfpi, Dmfti, Dphifga, Dphifpi, Dphifti), and addingthe products of the multiplications. Further, the fuel injection amountcommand value Mfcmd and the fuel injection timing command value φfcmdare calculated by adding the correction values Mfcr and φfcr,respectively, to the basic fuel injection amount Mfmap and the basicfuel injection timing φfmap. Subsequently, the fuel injection control isperformed by the calculated command values. Therefore, even if theintake gas state parameters GA, PI, and TI do not completely coincidewith the corresponding demand values or the reference value, appropriatecommand values of the fuel injection amount and the fuel injectiontiming are obtained according to the deviations δGa, δPi, and δTi andaccurate fuel injection control is performed. Further, since thecorrection values Mfcr and φfcr are calculated by multiplying the changerate parameters by the deviations δGa, δPi, and δTi, the number ofset-points in the maps for calculating the fuel injection amount and thefuel injection timing suitable for the actual intake gas state parametervalues is reduced. Accordingly, accurate fuel injection control isrealized while suppressing the memory capacity and the manpower forsetting the maps.

Further, by including the intake gas temperature TI in the intake gasstate parameters, the control is performed in view of the influence of achange in the intake gas temperature, thereby improving accuracy of thecontrol.

Further, the fuel injection amount command value Mfcmd and the fuelinjection timing command value φfcmd are calculated using the maps setcorresponding to the combustion modes. Accordingly, the optimal controlvalues are obtained corresponding to each combustion mode.

When at least one of the absolute values of the fresh air flow ratedeviation δGa and the intake pressure deviation δPi is greater than thepredetermined threshold values, immediately after the change in thecombustion mode parameter Mdcmb to a value corresponding to the richcombustion mode or the premix combustion mode, the modified combustionmode parameter FMdcmb is maintained at the value before the change (FIG.13, steps 34, S36), and the control maps corresponding to the combustionmode before the change are used. When both of the absolute values of thefresh air flow rate deviation δGa and the intake pressure deviation δPibecome less than the predetermined threshold values, the modifiedcombustion mode parameter FMdcmb is made to coincide with the combustionmode parameter Mdcmb (FIG. 13, steps S35, S37), and the control mapscorresponding to the changed combustion mode are used. In the transientstate after changing the combustion mode, the fresh air flow ratedeviation δGa and the intake pressure deviation δPi tend to becomelarge. Accordingly, the control is stabilized by using the control mapscorresponding to the combustion mode before the change until thedeviations become small.

In this embodiment, the fuel injection valve 9 corresponds to the fuelinjection means. The intake air flow rate sensor 21, the intake gastemperature sensor 23, and the intake pressure sensor 24 correspond tothe intake gas state parameter detecting means. The throttle valve 3,the EGR valve 6, and the movable vane 12 form a portion of the intakegas state control means, and the ECU 20 includes the combustion modedetermining means, the demand value calculating means, the intake gastemperature reference value calculating means, a portion of the intakegas state control means, and the fuel injection control means.Specifically, the combustion mode determination block 41 corresponds tothe combustion mode determining means. The intake gas state parameterdemand value setting block 42 corresponds to the demand valuecalculating means and the intake gas temperature reference valuecalculating means. The intake gas state control block 43 corresponds toa portion of the intake gas state control means, and the fuel injectioncontrol block 44 corresponds to the fuel injection control means.

Second Embodiment

In this embodiment, the demand fresh air flow rate Giades, the demandintake pressure Pides, and a demand intake oxygen partial pressurePiodes are calculated according to the engine rotational speed NE andthe demand torque TRQ. Also, intake gas state control is performed torealize the demand intake pressure Pides and the demand intake oxygenpartial pressure Piodes. Further, the fuel injection controlcorresponding to the demand intake pressure Pides and the demand intakeoxygen partial pressure Piodes is performed. The demand intake oxygenpartial pressure Piodes is a demand value of a partial pressure ofoxygen in the intake gases (hereinafter referred to as “intake oxygenpartial pressure”). In this embodiment, the demand fresh air flow rateGiades is applied only to the calculation of the target power Wcref ofthe compressor wheel 15 in the intake gas state control block, i.e., thedemand fresh air flow rate Giades does not correspond to the “intake gasstate parameter” described in the claims.

In order to perform a control contemplating the intake oxygen partialpressure, an intake oxygen concentration sensor 30 for detecting anoxygen concentration CIO in the intake gases is provided in the intakepipe 2 as shown in FIG. 15. Further, an exhaust oxygen concentrationsensor 26 for detecting an oxygen concentration CEO in the exhaust gasesis provided between the turbine 11 and the catalytic converter 31 in theexhaust pipe 4.

FIG. 16 is a block diagram showing a configuration of a control modulewhich performs the intake gas state control and the fuel injectioncontrol in this embodiment. The control module includes the combustionmode determination block 41, an intake gas state parameter demand valuesetting block 42 a, an intake gas state control block 43 a, and a fuelinjection control block 44 a. The combustion mode determination block 41is the same as the combustion mode determination block of the firstembodiment (FIG. 2).

The intake gas state parameter demand value setting block 42 a includes,as shown in FIG. 17, a first demand value setting block 101 a, a seconddemand value setting block 102 a, a third demand value setting block 103a, and switching blocks 104, 105, and 106 a. The switching blocks 104,105 are the same as the switching blocks 104, 105 shown in FIG. 3.

The first demand value setting block 101 a retrieves the Giades1 map,the Pides1 map, and the Piodes1 map suitable for the lean combustionmode according to the engine rotational speed NE and the demand torqueTRQ to calculate the first demand fresh air flow rate Giades1, the firstdemand intake pressure Pides1, and a first demand intake oxygen partialpressure Piodes1. The second demand value setting block 102 a retrievesthe Giades2 map, the Pides2 map, and the Piodes2 map suitable for therich combustion mode according to the engine rotational speed NE and thedemand torque TRQ to calculate the second demand fresh air flow rateGiades2, the second demand intake pressure Pides2, and a second demandintake oxygen partial pressure Piodes2. The third demand value settingblock 103 a retrieves the Giades3 map, Pides3 map, and Piodes3 mapsuitable for the premix combustion mode according to the enginerotational speed NE and the demand torque TRQ to calculate the thirddemand fresh air flow rate Giades3, the third demand intake pressurePides3, and a third demand intake oxygen partial pressure Piodes3.

The switching block 106 a selects one of the first-to-third demandintake oxygen partial pressures Piodes1, Piodes2, and Piodes3 accordingto the combustion mode parameter Mdcmb and outputs the selected one asthe demand intake oxygen partial pressure Piodes. If Mdcmb is equal to“1”, the first demand intake oxygen partial pressure Piodes1 isselected. If Mdcmb is equal to “2”, the second demand intake oxygenpartial pressure Piodes2 is selected. If Mdcmb is equal to “3”, thethird demand intake oxygen partial pressure Piodes3 is selected.

The intake gas state control block 43 a is configured as shown in FIG.18. That is, the intake gas state control block 43 a is obtained bydeleting the demand recirculated gas partial pressure calculation block51 and the subtracting block 58 in the intake gas state control block 43shown in FIG. 4, changing the dividing block 52, the multiplying block57, and the model predictive controller 60, respectively, to a dividingblock 52 a, a multiplying block 57 a, and a model predictive controller60 a, and adding a multiplying block 57 b.

The dividing block 52 a divides the demand intake oxygen partialpressure Piodes by the demand intake pressure Pides to calculate ademand intake oxygen ratio RPIO. The multiplying block 57 a multipliesthe target intake pressure Piref by the demand intake oxygen ratio RPIOto calculate a target intake oxygen partial pressure Pioref. Themultiplying block 57 b multiplies the detected intake pressure PI by thedetected intake oxygen concentration CIO to calculate an intake oxygenpartial pressure PIO.

The target exhaust pressure Peref, the detected exhaust pressure PE, thetarget intake pressure Piref, the detected intake pressure PI, thetarget intake oxygen partial pressure Pioref, the detected intake oxygenpartial pressure PIO, and the detected exhaust oxygen concentration CEOare supplied to the model predictive controller 60 a. The modelpredictive controller 60 a calculates the turbine gas flow rate commandvalue Gvcmd, the fresh air flow rate command value Gthcmd, and therecirculated gas flow rate command value Grcmd using the modelpredictive control so that the detected exhaust pressure PE, thedetected intake pressure PI, and the detected intake oxygen partialpressure PIO coincide, respectively, with the target exhaust pressurePeref, the target intake pressure Piref, and the target intake oxygenpartial pressure Pioref.

Next, the model of the intake gas state control system in thisembodiment is described below.

Regarding the intake pressure Pi, equation (201) is satisfied. Since theintake gas flow rate G′z is expressed by equation (24) (shown again),equation (202) is obtained by applying equation (24) to equation (201).

$\begin{matrix}{{\frac{\mathbb{d}}{\mathbb{d}t}{Pi}} = {{ki}\left( {{G^{\prime}{th}} + {G^{\prime}r} - {G^{\prime}z}} \right)}} & (201) \\{{G^{\prime}z} = {k_{\eta\; v}^{\prime} \times {Pi}}} & (24) \\{{\frac{\mathbb{d}}{\mathbb{d}t}{Pi}} = {{{- k_{\eta\; v}^{\prime}}{{ki} \cdot {Pi}}} + {{ki}\left( {{G^{\prime}{th}} + {G^{\prime}r}} \right)}}} & (202)\end{matrix}$

Regarding the intake oxygen partial pressure Pio, equation (203) issatisfied. In equation (203), “Mio” is a mass of the oxygen in theintake pipe.Pio×Vi=Mio×R×Ti  (203)

By differentiating equation (203) with respect to time, equation (204)is obtained. Further, if a ratio of oxygen contained in air is expressedby “rao” and a ratio of oxygen contained in exhaust gases is expressedby “reo”, equation (205) is satisfied. The oxygen ratio rao in air is aconstant (0.232), and the detected exhaust oxygen concentration CEO isused as the oxygen ratio reo.

$\begin{matrix}{\frac{\mathbb{d}{Pio}}{\mathbb{d}t} = {\kappa\;{ni}\frac{{RT}\; i}{Vi}\frac{\mathbb{d}{Mio}}{\mathbb{d}t}}} & (204) \\{\frac{\mathbb{d}{Mio}}{\mathbb{d}t} = {{{{rao} \cdot G^{\prime}}{th}} + {{{reo} \cdot G^{\prime}}r} - {{\frac{Pio}{Pi} \cdot G^{\prime}}z}}} & (205)\end{matrix}$

By applying equations (205) and (24) to equation (204), equation (206)is obtained.

$\begin{matrix}{{\frac{\mathbb{d}}{\mathbb{d}t}{Pio}} = {{{- k_{\eta\; v}^{\prime}}{{ki} \cdot {Pio}}} + {{ki}\left( {{{{rao} \cdot G^{\prime}}{th}} + {{{reo} \cdot G^{\prime}}r}} \right)}}} & (206)\end{matrix}$

Regarding the exhaust pressure Pe, equation (28) (shown again) issatisfied. By applying equation (24) to equation (28), equation (207) isobtained.

$\begin{matrix}{{{\frac{\mathbb{d}}{\mathbb{d}t}{Pe}} = {{ke}\left( {{G^{\prime}z} - {G^{\prime}r} - {G^{\prime}v}} \right)}}\left( {{ke} = {\kappa\;{ne}\frac{RTe}{Ve}}} \right)} & (28) \\{{\frac{\mathbb{d}}{\mathbb{d}t}{Pe}} = {{k_{\eta\; v}^{\prime}{{ke} \cdot {Pi}}} - {{ke}\left( {{G^{\prime}r} + {G^{\prime}v}} \right)}}} & (207)\end{matrix}$

By combining equations (202), (206), and (207), and converting thecombined equation to an equation based on the crank angle α, equation(208), which defines the controlled object model, is obtained.Therefore, the control input u(k) is calculated based on equation (208)with the same method as the first embodiment described above.

$\begin{matrix}{{\frac{\mathbb{d}}{\mathbb{d}\alpha}\left\lbrack \begin{matrix}{Pi} \\{Pio} \\{Pe}\end{matrix} \right\rbrack} = \mspace{70mu}{{{\left\lbrack \begin{matrix}{{- k_{\eta\; v}}{ki}} & 0 & 0 \\0 & {{- k_{\eta\; v}}{ki}} & 0 \\{k_{\eta\; v}{ke}} & 0 & 0\end{matrix} \right\rbrack\left\lbrack \begin{matrix}{Pi} \\{Pio} \\{Pe}\end{matrix} \right\rbrack} + {{\left\lbrack \begin{matrix}{ki} & {ki} & 0 \\{{ki} \cdot {rao}} & {{ki} \cdot {reo}} & 0 \\0 & {- {ke}} & {- {ke}}\end{matrix} \right\rbrack\left\lbrack \begin{matrix}u_{th} \\u_{r} \\u_{v}\end{matrix} \right\rbrack}\mspace{20mu}\begin{bmatrix}u_{th} \\u_{r} \\u_{v}\end{bmatrix}}} = \begin{bmatrix}{Gth} & {Gr} & {Gv}\end{bmatrix}^{T}}} & (208)\end{matrix}$

FIG. 19 is a block diagram showing a configuration of the fuel injectioncontrol block 44 a of FIG. 17. The fuel injection control block 44 aincludes a deviation calculation block 111 a, a transient control block112 a, a first command value calculation block 113 a, a second commandvalue calculation block 114 a, a third command value calculation block115 a, the switching blocks 116 and 117, and a multiplying block 118.The switching blocks 116 and 117 operate similarly as the blocks shownin FIG. 10.

The multiplying block 118 multiplies the intake oxygen concentration CIOby the intake pressure PI to calculate the intake oxygen partialpressure PIO. The deviation calculation block 111 a calculates an intakeoxygen partial pressure deviation δPio and the intake pressure deviationδPi by equations (211) and (212).δPio=PIO−Piodes  (211)δPi=PI−Pides  (212)

The transient control block 112 a calculates the modified combustionmode parameter FMdcmb according to the combustion mode parameter Mdcmb,the intake oxygen partial pressure deviation δPio, and the intakepressure deviation δPi. When the operating condition of the engine 1 isin a steady state, the modified combustion mode parameter FMdcmb isequal to the combustion mode parameter Mdcmb. When the combustion modeparameter Mdcmb is changed (for example, when changed from “1” to “2”),the modified combustion mode parameter FMdcmb is maintained at thepreceding value (“1”) if at least one of the intake oxygen partialpressure deviation δPio and the intake pressure deviation δPi is equalto or greater than a predetermined deviation amount. When both of theintake oxygen partial pressure deviation δPio and the intake pressuredeviation δPi become less than the corresponding predetermined deviationamounts, the modified combustion mode parameter FMdcmb is set to thechanged combustion mode parameter Mdcmb (“2”).

The first command value calculation block 113 a calculates the firstfuel injection amount Mfcmd1 and the first fuel injection timing φfcmd1suitable for the lean combustion mode according to the demand torqueTRQ, the engine rotational speed NE, the intake oxygen partial pressuredeviation δPio, and the intake pressure deviation δPi. The secondcommand value calculation block 114 a calculates the second fuelinjection amount Mfcmd2 and the second fuel injection timing φfcmd2suitable for the rich combustion mode according to the demand torqueTRQ, the engine rotational speed NE, the intake oxygen partial pressuredeviation δPio, and the intake pressure deviation δPi. The third commandvalue calculation block 115 a calculates the third fuel injection amountMfcmd3 and the third fuel injection timing φfcmd3 suitable for thepremix combustion mode according to the demand torque TRQ, the enginerotational speed NE, the intake oxygen partial pressure deviation δPio,and the intake pressure deviation δPi.

FIG. 20 is a block diagram showing a configuration of the first commandvalue calculation block 113 a. The first command value calculation block113 a includes the first and second basic value calculation blocks 121and 141; first and second oxygen partial pressure change rate parametercalculation blocks 122 a and 142 a; first and second pressure changerate parameter calculation blocks 123 and 143; multiplying blocks 125 a,126, 145 a, and 146; and adding blocks 129 a, 130,149 a, and 150. Theblocks with the same reference numerals of the blocks shown in FIG. 11have the same function as the blocks shown in FIG. 11, wherein only thedifferences between the two embodiments will be described below.

The first oxygen partial pressure change rate parameter calculationblock 122 a retrieves a Dmfpio1 map according to the demand torque TRQand the engine rotational speed NE to calculate a first oxygen partialpressure change rate parameter Dmfpio1. In the above-described Dmfpio1map, values suitable for the lean combustion mode are set, and gridpoints of the map defined by the demand torque TRQ and the enginerotational speed NE are set to be the same as the grid points of the mapused in the first demand value setting block 101 a.

The multiplying block 125 a multiplies the first oxygen partial pressurechange rate parameter Dmfpio1 by the intake oxygen partial pressuredeviation δPio. The adding block 129 a adds the outputs of themultiplying blocks 125 a and 126 to calculate the first fuel injectionamount correction value Mfcr1.

The second oxygen partial pressure change rate parameter calculationblock 142 a retrieves a Dφfpio1 map according to the demand torque TRQand the engine rotational speed NE to calculate a second oxygen partialpressure change rate parameter Dφfpio1. In the above-described Dφfpio1map, values suitable for the lean combustion mode are set, and gridpoints of the map defined by the demand torque TRQ and the enginerotational speed NE are set to be the same as the grid points of the mapused in the first demand value setting block 101 a.

The multiplying block 145 a multiplies the second oxygen partialpressure change rate parameter Dφfpio1 by the intake oxygen partialpressure deviation δPio. The adding block 149 a adds the outputs of themultiplying blocks 145 a and 146 to calculate the first fuel injectiontiming correction value φfcr1.

Therefore, the calculations of the first fuel injection amount Mfcmd1and the first fuel injection timing φfcmd1 in the first command valuecalculation block 113 a are, respectively, expressed by equations (213)and (214).

$\begin{matrix}\begin{matrix}{{{Mfcmd}\; 1} = {{{Mf}\; 1} + {{Mfcr}\; 1}}} \\{= {{{Mf}\; 1} + {\delta\;{Pio} \times {Dmfpio}\; 1} + {\delta\;{Pi} \times {Dmfpi}\; 1}}}\end{matrix} & (213) \\\begin{matrix}{{\phi\;{fcmd}\; 1} = {{\phi\; f\; 1} + {\phi\;{fcr}\; 1}}} \\{= {{\phi\; f\; 1} + {\delta\;{Pio} \times D\;\phi\;{fpio}\; 1} + {\delta\;{Pi} \times D\;\phi\;{fpi}\; 1}}}\end{matrix} & (214)\end{matrix}$

The second command value calculation block 114 a and the third commandvalue calculation block 115 a shown in FIG. 19 are configured similarlyto the first command value calculation block 113 a. The second fuelinjection amount Mfcmd2, the second fuel injection timing φfcmd2, thethird fuel injection amount Mfcmd3, and the third fuel injection timingφfcmd3 are, respectively, calculated by equations (215)-(218).

$\begin{matrix}\begin{matrix}{{{Mfcmd}\; 2} = {{{Mf}\; 2} + {{Mfcr}\; 2}}} \\{= {{{Mf}\; 2} + {\delta\;{Pio} \times {Dmpio}\; 2} + {\delta\;{Pi} \times {Dmfpi}\; 2}}}\end{matrix} & (215) \\\begin{matrix}{{\phi\;{fcmd}\; 2} = {{\phi\; f\; 2} + {\phi\;{fcr}\; 2}}} \\{= {{\phi\; f\; 2} + {\delta\;{Pio} \times D\;\phi\;{pio}\; 2} + {\delta\;{Pi} \times D\;\phi\;{fpi}\; 2}}}\end{matrix} & (216) \\\begin{matrix}{{{Mfcmd}\; 3} = {{{Mf}\; 3} + {{Mfcr}\; 3}}} \\{= {{{Mf}\; 3} + {\delta\;{Pio} \times {Dmpio}\; 3} + {\delta\;{Pi} \times {Dmfpi}\; 3}}}\end{matrix} & (217) \\\begin{matrix}{{\phi\;{fcmd}\; 3} = {{\phi\; f\; 3} + {\phi\;{fcr}\; 3}}} \\{= {{\phi\; f\; 3} + {\delta\;{Pio} \times D\;\phi\;{pio}\; 3} + {\delta\;{Pi} \times D\;\phi\;{fpi}\; 3}}}\end{matrix} & (218)\end{matrix}$

FIGS. 21 and 22 show a flowchart of a process for executing the intakegas state control and the fuel injection control described above. Theprocess is obtained by replacing steps S14-S21, S31, S34, S36, andS39-S43 of the process shown in FIGS. 12 and 13, respectively, withsteps S14 a-S21 a, S31 a, S34 a, S36 a, and S39 a-S43 a, and adding stepS20 b.

In step S14 a, the Giades1 map, the Pides1 map, and the Piodes1 map areretrieved according to the engine rotational speed NE and the demandtorque TRQ to calculate the first demand fresh air flow rate Giades1,the first demand intake pressure Pides1, and a first demand intakeoxygen partial pressure Piodes1. Subsequently, the demand fresh air flowrate Giades, the demand intake pressure Pides, and the demand intakeoxygen partial pressure Piodes are, respectively, set to the calculatedvalues of the first demand fresh air flow rate Giades1, the first demandintake pressure Pides1, and the first demand intake oxygen partialpressure Piodes1 (step S15 a).

In step S16 a, the Giades2 map, the Pides2 map, and the Piodes2 map areretrieved according to the engine rotational speed NE and the demandtorque TRQ to calculate the second demand fresh air flow rate Giades2,the second demand intake pressure Pides2, and a second demand intakeoxygen partial pressure Piodes2. Subsequently, the demand fresh air flowrate Giades, the demand intake pressure Pides, and the demand intakeoxygen partial pressure Piodes are, respectively, set to the calculatedvalues of the second demand fresh air flow rate Giades2, the seconddemand intake pressure Pides2, and the second demand intake oxygenpartial pressure Piodes2 (step S17 a).

In step S18 a, the Giades3 map, the Pides3 map, and the Piodes3 map areretrieved according to the engine rotational speed NE and the demandtorque TRQ to calculate the third demand fresh air flow rate Giades3,the third demand intake pressure Pides3, and a third demand intakeoxygen partial pressure Piodes3. Subsequently, the demand fresh air flowrate Giades, the demand intake pressure Pides, and the demand intakeoxygen partial pressure Piodes are, respectively, set to the calculatedvalues of the third demand fresh air flow rate Giades3, the third demandintake pressure Pides3, and the third demand intake oxygen partialpressure Piodes3 (step S19 a).

In step S20 a, the detected parameters, such as the intake oxygenconcentration CIO and the intake pressure PI, are obtained. In step S21a, the intake oxygen partial pressure PIO is calculated by multiplyingthe intake oxygen concentration CIO by the intake pressure PI.

In step S21 a, the intake gas state control described with reference toFIG. 18 is performed, and the vane opening command value θvcmd, thethrottle valve opening command value θthcmd, and the EGR valve openingcommand value θrcmd are calculated.

Next, in step S31 a of FIG. 22, the intake oxygen partial pressuredeviation δPio and the intake pressure deviation δPi are calculated.

In step S34 a, it is determined whether the absolute value of the intakeoxygen partial pressure deviation δPio is less than a 5th predeterminedthreshold value εpio2 (for example, 0.05×Piodes), and the absolute valueof the intake pressure deviation δPi is less than the secondpredetermined threshold value εpi2 (for example, 0.05×Pides). If theanswer to step S34 a is negative (NO), i.e., when |δPio| is greater thanor equal to εpio2, or |δPi| is greater than or equal to εpi2, theprocess proceeds to step S38 without changing the value of the modifiedcombustion mode parameter FMdcmb (holding the preceding value). On theother hand, if the answer to step S34 a is affirmative (YES), themodified combustion mode parameter FMdcmb is set to “2” (step S35) andthe process proceeds to step S38.

In step S36 a, it is determined whether the absolute value of the intakeoxygen partial pressure deviation δPio is less than a 6th predeterminedthreshold value εpio3 (for example, 0.05×Piodes), and the absolute valueof the intake pressure deviation δPi is less than the 4th predeterminedthreshold value εpi3 (for example, 0.05×Pides). If the answer to stepS36 a is negative (NO), i.e., when |δPio| is greater than or equal toεpio3, or |δPi| is greater than or equal to εpi3, the process proceedsto step S38 without changing the value of the modified combustion modeparameter FMdcmb (holding the preceding value). On the other hand, ifthe answer to step S36 a is affirmative (YES), the correction combustionmode parameter FMdcmb is set to “3” (step S37) and the process proceedsto step S38.

A first fuel injection command value map retrieval process correspondingto the lean combustion mode is performed in step S39 a. A second fuelinjection command value map retrieval process corresponding to the richcombustion mode is performed in step S40 a. Finally, a third fuelinjection command value map retrieval process corresponding to thepremix combustion mode is performed in step S41 a.

FIG. 23 is a flowchart of the retrieval process performed in step S39 a.The process is obtained by replacing steps S53, S54, S61, and S62 of theprocess shown in FIG. 14, respectively, with steps S53 a, S54 a, S61 a,and S62 a, and deleting steps S57, S58, S65, and S66.

In step S53 a, the Dmfpio1 map is retrieved according to the enginerotational speed NE and the demand torque TRQ to calculate a firstoxygen partial pressure change rate parameter Dmfpio1, and the oxygenpartial pressure change rate parameter Dmfpio is set to the first oxygenpartial pressure change rate parameter Dmfpio1 (step S54 a).

In step S61 a, the Dφfpio1 map is retrieved according to the enginerotational speed NE and the demand torque TRQ to calculate a secondoxygen partial pressure change rate parameter Dφfpio1. The oxygenpartial pressure change rate parameter Dφfpio is set to the secondoxygen partial pressure change rate parameter Dφfpio1 in step S62 a.

In the process of FIG. 23, the basic fuel injection amount Mfmap, thefirst oxygen partial pressure change rate parameter Dmfpio, the firstpressure change rate parameter Dmfpi, the basic fuel injection timingφfmap, the second oxygen partial pressure change rate parameter Dφfpio,and the second pressure change rate parameter Dφfpi suitable for thelean combustion mode are calculated.

Referring back to FIG. 22, the second fuel injection command value mapretrieval process and the third fuel injection command value mapretrieval process in steps S40 a and S41 a are configured similarly tothe first fuel injection command value map retrieval process shown inFIG. 23. That is, in the second fuel injection command value mapretrieval process, the basic fuel injection amount Mfmap, the firstoxygen partial pressure change rate parameter Dmfpio, the first pressurechange rate parameter Dmfpi, the basic fuel injection timing φfmap, thesecond oxygen partial pressure change rate parameter Dφfpio, and thesecond pressure change rate parameter Dφfpi suitable for the richcombustion mode are calculated. In the third fuel injection commandvalue map retrieval process, the basic fuel injection amount Mfmap, thefirst oxygen partial pressure change rate parameter Dmfpio, the firstpressure change rate parameter Dmfpi, the basic fuel injection timingφfmap, the second oxygen partial pressure change rate parameter Dφfpio,and the second pressure change rate parameter Dφfpi suitable for thepremix combustion mode are calculated.

In step S42 a, the fuel injection amount correction value Mfcr iscalculated by equation (219). In step S43 a, the fuel injection timingcorrection value φfcr is calculated by equation (220).Mfcr=δPio×Dmfpio+δPi×Dmfpi  (219)Φfcr=δPio×Dφfpio+δPi×Dφfpi  (220)

As described above, in this embodiment, the intake pressure PI and theintake oxygen partial pressure PIO (intake oxygen concentration CIO) aredetected as the intake gas state parameter. Also, the demand values ofthe intake gas state parameters, i.e., the demand intake pressure Pidesand the demand intake oxygen partial pressure Piodes, are calculatedaccording to the engine rotational speed NE and the demand torque TRQwhich indicate the engine operating condition. The intake gas state iscontrolled so that the intake pressure PI and the intake oxygen partialpressure PIO coincide, respectively, with the demand intake pressurePides and the demand intake oxygen partial pressure Piodes. Further, thefuel injection amount command value Mfcmd and the fuel injection timingcommand value φfcmd are calculated according to the engine rotationalspeed NE, the demand torque TRQ, and the deviations of the intakepressure PI and the intake oxygen partial pressure PIO from thecorresponding demand values (Pides, Piodes). The fuel injection valve 9is then controlled according to the calculated command values.Therefore, the desired intake gas state according to the engineoperating condition is realized, and the control of the fuel injectionamount and the fuel injection timing suitable for the intake gas stateis performed, wherein good engine operating performance and good exhaustcharacteristics are obtained.

Specifically, the basic fuel injection amount Mfmap and the basic fuelinjection timing φfmap are calculated according to the engine rotationalspeed NE and the demand torque TRQ. The first pressure change rateparameter Dmfpi and the first oxygen partial pressure change rateparameter Dφfpio, which indicate the change rate of the basic fuelinjection amount Mfmap, are calculated according to the enginerotational speed NE and the demand torque TRQ. Further, the secondpressure change rate parameter Dφfpi and the second oxygen partialpressure change rate parameter Dφfpio, which indicate the change rate ofthe basic fuel injection timing φfmap, are calculated according to theengine rotational speed NE and the demand torque TRQ. Further, thecorrection values Mfcr and φfcr are calculated by multiplying the intakepressure deviation δPi and the oxygen partial pressure deviation δPio,which indicate the deviations of the detected intake gas stateparameters from the demand values, by the corresponding change rateparameters (Dmfpi, Dmfpio, Dφfpi, and Dφfpio), and adding the productsof the multiplications. The correction values Mfcr and φfcr are,respectively, added to the basic fuel injection amount Mfmap and thebasic fuel injection timing φfmap to calculate the fuel injection amountcommand value Mfcmd and the fuel injection timing command value φfcmd.Subsequently, the fuel injection control is performed based on thecalculated command values. Therefore, even if the intake gas stateparameters PI and PIO do not completely coincide with the correspondingdemand values, appropriate command values of the fuel injection amountand the fuel injection timing are obtained according to the deviationsδPi and δPio and accurate fuel injection control is performed. Further,since the correction values Mfcr and φfcr are calculated by multiplyingthe change rate parameters by the deviations δPi and δPio, the number ofset-points in the maps for calculating the fuel injection amount and thefuel injection timing suitable for the actual intake gas state parametervalues, is reduced. Accordingly, accurate fuel injection control isrealized, and memory capacity and manpower for setting the maps aresuppressed.

In this embodiment, the intake pressure sensor 24 and the intake oxygenconcentration sensor 30 correspond to the intake gas state parameterdetecting means. The throttle valve 3, the EGR valve 6, and the movablevane 12 correspond to a part of the intake gas state control means, andthe ECU 20 corresponds to the combustion mode determining means, thedemand value calculating means, a portion of the intake gas statecontrol means, and the fuel injection control means. Specifically, thecombustion mode determination block 41 corresponds to the combustionmode determining means, the intake gas state parameter demand valuesetting block 42 a corresponds to the demand value calculating means,the intake gas state control block 43 a corresponds to a portion of theintake gas state control means, and the fuel injection control block 44a corresponds to the fuel injection control means.

The present invention is not limited to the embodiments described above,and various modifications may be made thereto. For example, in the firstembodiment, the intake pressure PI, the recirculated gas flow rate GRand the intake gas temperature TI, or the intake air flow rate GA(intake fresh air flow rate), the recirculated gas flow rate GR, and theintake gas temperature TI may be used as the intake gas stateparameters. Further, in the second embodiment, the intake pressure PIand a partial pressure PII of the inert gases in the intake gases, orthe intake oxygen partial pressure PIO and the inert gas partialpressure PII may be used as the intake gas state parameters. Also, inertgases can be the gases contained in the intake gases other than oxygen.

The reason why the fuel injection control is appropriately performedusing the intake gas state parameters is described below.

In order to appropriately perform the fuel injection control, it isnecessary to control an oxygen mass Mo and an inert gas mass Mi in thecombustion chamber to desired values. The intake pressure PI is equal tothe sum of the intake oxygen partial pressure PIO and the intake inertgas partial pressure PII, as shown in equation (301).PI=PIO+PII  (301)

The total gas mass Mt in the combustion chamber is equal to the sum ofthe oxygen mass Mo and the inert gas mass Mi in the combustion chamber.Further, if the relationship of the above-described equation (20)(PV=MRT) and the volumetric efficiency of the engine are taken intoconsideration, the intake pressure PI, the intake oxygen partialpressure PIO, and the intake inert gas partial pressure PII can beexpressed by equations (302)-(304).PI=kEV×Mt  (302)PIO=kEV×Mo  (303)PII=kEV×Mi  (304)where kEV is a coefficient calculated in view of the relationship ofequation (20) and the volumetric efficiency of the engine.

Therefore, in order to control the oxygen mass Mo and the inert gas massMi to the corresponding desired values, any two of the intake pressurePI, the intake oxygen partial pressure PIO, and the intake inert gaspartial pressure PII may be controlled to the corresponding demandvalues. This is because if any two are determined, the remaining onewill be determined from the relationship of equation (301).

The intake inert gas partial pressure PII can be obtained by subtractingthe detected intake oxygen partial pressure PIO from the detected intakepressure PI.

On the other hand, the intake pressure PI can also be expressed by a sumof the fresh air partial pressure PIA and the recirculated gas partialpressure PIR as shown in equation (305).PI=PIA+PIR  (305)

Further, the intake oxygen partial pressure PIO and the intake inert gaspartial pressure PII can be expressed by equations (306) and (307).“reo” and “rao” in these equations are an oxygen ratio in the exhaustgases, and an oxygen ratio in the air, respectively.PIO=reo×PIR+rao×PIA  (306)PII=(1−reo)×PIR+(1−rao)×PIA  (307)

If the relationships shown by equations (305)-(307) are used, the oxygenmass Mo and the inert gas mass Mi can be controlled to the correspondingdesired values by controlling any two of the intake pressure PI, thefresh air partial pressure PIA, and the recirculated gas partialpressure PIR. That is, any two of the intake pressure PI, the fresh airpartial pressure PIA, and the recirculated gas partial pressure PIR maybe adopted as the intake gas state parameters.

However, since it is rather difficult to directly detect the fresh airpartial pressure PIA and the recirculated gas partial pressure PIR, itis preferable to use the fresh air flow rate, i.e., the intake air flowrate GA, and the recirculated gas flow rate GR, which are detectableparameters relating to the fresh air partial pressure PIA and therecirculated gas partial pressure PIR. Since the intake pressure PI, thefresh air partial pressure PIA, and the recirculated gas partialpressure PIR can be expressed by equations (308)-(310) (refer toequations (24) and (26)), the intake air flow rate GA and therecirculated gas flow rate GR can be used alternatively as the intakegas state parameters.PI=k _(η) v×GZ  (308)PIA=k _(η) v×GA  (309)PIR=k _(η) v×GR  (310)

In equation (308), GZ is an intake gas flow rate obtained by adding theintake air flow rate GA and the recirculated gas flow rate GR. Therecirculated gas flow rate GR in equation (310) can be calculated bysubtracting the intake air flow rate GA from the intake gas flow rate GZcalculated using the relationship of equation (308).

In the above-described embodiments, examples where the present inventionis applied to the control of a diesel internal combustion engine areshown. The present invention is applicable also to a gasoline internalcombustion engine. With respect to the gasoline internal combustionengine, the present invention is also applicable to an engine in whichfuel is injected into the intake pipe.

The present invention can be applied to a control system for awatercraft propulsion engine, such as an outboard engine having avertically extending crankshaft.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresently disclosed embodiments are therefore to be considered in allrespects as illustrative and not restrictive, the scope of the inventionbeing indicated by the appended claims, rather than the foregoingdescription, and all modifications which come within the meaning andrange of equivalency of the claims are, therefore, to be embracedtherein.

1. A control system for an internal combustion engine having fuelinjection means for injecting fuel to an intake pipe or a combustionchamber of said engine, comprising: intake gas state parameter detectingmeans for detecting intake gas state parameters indicative of a state ofintake gases supplied to said engine; demand value calculating means forcalculating demand values of the intake gas state parameters accordingto operating condition parameters indicative of an operating conditionof said engine; intake gas state control means for controlling theintake gas state so that the intake gas state parameters coincide withthe demand values; and fuel injection control means for calculating acontrol value according to the operating condition parameters anddeviations of the intake gas state parameters from the demand values,and for controlling an amount of fuel injected by said fuel injectionmeans according to the control value.
 2. The control system according toclaim 1, wherein said fuel injection control means controls a fuelinjection timing of said fuel injection means according to the operatingcondition parameters and the deviations of the intake gas stateparameters from the demand values.
 3. The control system according toclaim 1, wherein said fuel injection control means comprises: basiccontrol value calculating means for calculating a basic control valueaccording to the operating condition parameters; change rate parametercalculating means for calculating change rate parameters indicative ofchange rates of the basic control value according to the operatingcondition parameters; correction value calculating means for calculatingcorrection values by multiplying the change rate parameters by thedeviations of the intake gas state parameters from the demand values;and control value calculating means for calculating the control value ofthe fuel injection amount by correcting the basic control value with thecorrection values, wherein said fuel injection control means performsthe fuel injection control according to the control value calculated bysaid control value calculating means.
 4. The control system for aninternal combustion engine according to claim 1, wherein the intake gasstate parameters are any two of an intake pressure, an intake oxygenpartial pressure, and an intake inert gas partial pressure.
 5. Thecontrol system according to claim 1, wherein said engine comprises anexhaust gas recirculation mechanism for recirculating exhaust gases tosaid intake pipe, and the intake gas state parameters are any two of anintake pressure, an intake fresh air flow rate, and a flow rate ofrecirculated exhaust gases.
 6. The control system according to claim 4,wherein an intake gas temperature is further included in the intake gasstate parameters, wherein said control system further comprises intakegas temperature reference value calculating means for calculating areference value of the intake gas temperature, and wherein said fuelinjection control means performs the fuel injection control according toa deviation of a detected intake gas temperature from the referencevalue.
 7. The control system according to claim 1, further comprisingcombustion mode determining means for determining a combustion mode ofsaid engine according to the operating condition parameters, whereinsaid fuel injection control means calculates the control value using acontrol map set corresponding to the combustion mode.
 8. The controlsystem according to claim 7, wherein when said combustion modedetermining means changes the combustion mode, said fuel injectioncontrol means uses the control map corresponding to the combustion modebefore the combustion mode is changed if at least one of absolute valuesof the deviations is equal to or greater than a predetermined thresholdvalue, and said fuel injection control means uses the control mapcorresponding to the changed combustion mode if each of the absolutevalues of the deviations is less than the predetermined threshold value.9. The control system according to claim 1, wherein said engine has athrottle valve disposed in said intake pipe, an exhaust gasrecirculation mechanism for recirculating exhaust gases to said intakepipe, and a turbo charger having a compressor wheel and a turbine wheel,said exhaust gas recirculation mechanism including an exhaust gasrecirculation passage and an exhaust gas recirculation control valve insaid exhaust gas recirculation passage, said turbo charger includingmovable vanes for changing a flow rate of exhaust gases injected to saidturbine wheel, wherein said intake gas state control means controls theintake gas state by changing openings of said throttle valve, exhaustgas recirculation control valve, and movable vanes.
 10. The controlsystem according to claim 9, wherein said intake gas state control meanscontrols the intake gas state using a model predictive control.
 11. Thecontrol system according to claim 10, wherein a controlled object modelused in the model predictive control is defined using, as controlinputs, a mass flow rate of gases passing through said movable vanes, amass flow rate of gases passing through said exhaust gas recirculationcontrol valve, and a mass flow rate of fresh air passing through saidthrottle valve.
 12. A control method for an internal combustion enginehaving at least one fuel injection valve for injecting fuel to an intakepipe or a combustion chamber of said engine, said control methodcomprising the steps of: a) detecting intake gas state parametersindicative of a state of intake gases supplied to said engine; b)calculating demand values of the intake gas state parameters accordingto operating condition parameters indicative of an operating conditionof said engine; c) controlling the intake gas state so that the intakegas state parameters coincide with the demand values; d) calculating acontrol value according to the operating condition parameters anddeviations of the intake gas state parameters from the demand values;and e) controlling an amount of fuel injected by said at least one fuelinjection valve according to the control value.
 13. The control methodaccording to claim 12, wherein a fuel injection timing of said at leastone fuel injection valve is controlled according to the operatingcondition parameters and the deviations of the intake gas stateparameters from the demand values.
 14. The control method according toclaim 12, wherein said step d) includes the steps of: i) calculating abasic control value according to the operating condition parameters; ii)calculating change rate parameters indicative of change rates of thebasic control value according to the operating condition parameters;iii) calculating correction values by multiplying the change rateparameters by the deviations of the intake gas state parameters from thedemand values; and iv) calculating a control value of the fuel injectionamount by correcting the basic control value with the correction values,wherein the fuel injection control is performed according to thecalculated control value.
 15. The control method according to claim 12,wherein the intake gas state parameters are any two of an intakepressure, an intake oxygen partial pressure, and an intake inert gaspartial pressure.
 16. The control method according to claim 12, whereinsaid engine comprises an exhaust gas recirculation mechanism forrecirculating exhaust gases to said intake pipe, and the intake gasstate parameters are any two of an intake pressure, an intake fresh airflow rate, and a flow rate of recirculated exhaust gases.
 17. Thecontrol method according to claim 15, wherein an intake gas temperatureis further included in the intake gas state parameters, wherein saidcontrol method further includes the step of calculating a referencevalue of the intake gas temperature, and wherein the fuel injectioncontrol is performed according to a deviation of a detected intake gastemperature from the reference value.
 18. The control method accordingto claim 12, further comprising the step of determining a combustionmode of said engine according to the operating condition parameters,wherein the control value is calculated using a control map setcorresponding to the combustion mode.
 19. The control method accordingto claim 18, wherein when the combustion mode is changed, the controlmap corresponding to the combustion mode before the combustion mode ischanged is used if at least one of absolute values of the deviations isequal to or greater than a predetermined threshold value, and thecontrol map corresponding to the changed combustion mode is used if eachof the absolute values of the deviations is less than the predeterminedthreshold value.
 20. The control method according to claim 12, whereinsaid engine has a throttle valve disposed in said intake pipe, anexhaust gas recirculation mechanism for recirculating exhaust gases tosaid intake pipe, and a turbo charger having a compressor wheel and aturbine wheel, said exhaust gas recirculation mechanism including anexhaust gas recirculation passage and an exhaust gas recirculationcontrol valve in said exhaust gas recirculation passage, said turbocharger including movable vanes for changing a flow rate of exhaustgases injected to said turbine wheel, wherein the intake gas state iscontrolled by changing openings of said throttle valve, exhaust gasrecirculation control valve, and movable vanes.
 21. The control methodaccording to claim 20, wherein the intake gas state is controlled usinga model predictive control.
 22. The control method according to claim21, wherein a controlled object model used in the model predictivecontrol is defined using, as control inputs, a mass flow rate of gasespassing through said movable vanes, a mass flow rate of gases passingthrough said exhaust gas recirculation control valve, and a mass flowrate of fresh air passing through said throttle valve.